Population of quantum dots and a composition including the same

ABSTRACT

Disclosed are a quantum dot population including a plurality of cadmium free quantum dots, a quantum dot polymer composite including the same, and a display device including the same. The plurality of cadmium free quantum dots includes: a semiconductor nanocrystal core comprising indium and phosphorous, a first semiconductor nanocrystal shell disposed on the semiconductor nanocrystal core and comprising zinc and selenium, and a second semiconductor nanocrystal shell disposed on the first semiconductor nanocrystal shell and comprising zinc and sulfur, wherein an average particle size of the plurality of cadmium free quantum dots is greater than or equal to about 5.5 nm, a standard deviation of particle sizes of the plurality of cadmium free quantum dots is less than or equal to about 20% of the average particle size, and an average solidity of the plurality of cadmium free quantum dots is greater than or equal to about 0.85.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Korean Patent Application No.10-2018-0003831, filed in the Korean Intellectual Property Office onJan. 11, 2018, and all the benefits accruing therefrom under 35 U.S.C. §119, the content of which is incorporated herein in its entirety byreference.

BACKGROUND 1. Field

A population of quantum dots, a composition or composite including same,and an electronic device including the same are disclosed.

2. Description of the Related Art

Quantum dots (e.g., nano-sized semiconductor nanocrystals) havingdifferent energy bandgaps may be obtained by controlling their sizes andcompositions. Quantum dots may exhibit electroluminescent andphotoluminescent properties. In a colloidal synthesis, organic materialssuch as a dispersing agent may coordinate, e.g., be bound, to a surfaceof the semiconductor nanocrystal during the crystal growth thereof,thereby providing a quantum dot having a controlled size and havingluminescent properties. From an environmental standpoint, developing acadmium free quantum dot with improved luminescent properties isdesirable.

SUMMARY

An embodiment provides a population of cadmium free quantum dots thatmay exhibit improved photoluminescence properties (e.g., enhancedexcitation light absorption rate) and enhanced stability.

Another embodiment provides a method of producing the population of thecadmium free quantum dots.

Yet another embodiment provides a composition including the populationof cadmium free quantum dot.

Still another embodiment provides a quantum dot-polymer compositeincluding the population of cadmium free quantum dot.

Further another embodiment provides an electronic device including thequantum dot-polymer composite.

In an embodiment, a population of quantum dot includes a plurality ofcadmium free quantum dots, wherein the plurality of cadmium free quantumdots include a semiconductor nanocrystal core including indium (In) andphosphorous (P), a first semiconductor nanocrystal shell disposed on thesemiconductor nanocrystal core and including zinc and selenium, and asecond semiconductor nanocrystal shell disposed on the firstsemiconductor nanocrystal shell and including zinc and sulfur,

wherein an average particle size of the plurality of cadmium freequantum dots is greater than or equal to about 5.5 nanometers, astandard deviation of particle sizes of the plurality of cadmium freequantum dots is less than or equal to about 20% of the average particlesize, and an average solidity of the plurality of cadmium free quantumdots is greater than or equal to about 0.85.

The cadmium free quantum dots may include an organic ligand on a surfacethereof and the organic ligand may include a carboxylic acid compound(e.g., monocarboxylic acid compound) and a primary amine compound (e.g.,monoamine compound).

The carboxylic acid compound may have a C5 to C30 hydrocarbon group(e.g., a C5 to C30 aliphatic group), and a primary amine group of theprimary amine compound may have a C5 to C30 hydrocarbon group (e.g., aC5 to C30 aliphatic group).

The primary amine group may have a C5 to C30 alkenyl group.

The cadmium free quantum dots in an embodiment may not include boron.

The semiconductor nanocrystal core may further include zinc.

The first semiconductor nanocrystal shell may be disposed directly onthe surface of the semiconductor nanocrystal core.

The average particle size of the plurality of the cadmium free quantumdots may be greater than or equal to about 5.8 nanometers, for example,greater than or equal to about 6 nanometers.

The standard deviation of particle sizes of the plurality of cadmiumfree quantum dots may be less than or equal to about 18% of the averageparticle size.

The average solidity of the plurality of cadmium free quantum dots maybe greater than or equal to about 0.90.

A maximum photoluminescence peak of the plurality of cadmium freequantum dots may have a full width at half maximum of less than or equalto about 40 nm.

A quantum efficiency of the plurality of cadmium free quantum dots maybe greater than or equal to about 70%.

The first semiconductor nanocrystal shell may not include sulfur.

A thickness of the first semiconductor nanocrystal shell may be greaterthan or equal to about 3 monolayers.

A thickness of the first semiconductor nanocrystal shell may be lessthan or equal to about 10 monolayers.

The second semiconductor nanocrystal shell may be an outermost layer ofthe quantum dot.

The second semiconductor nanocrystal shell may be disposed directly onthe first semiconductor nanocrystal shell.

The second semiconductor nanocrystal shell may include ZnSeS, ZnS, or acombination thereof.

A molar ratio of a sum of sulfur and selenium with respect to indium[(Se+S)/In] may be greater than or equal to about 10:1, for example,greater than or equal to about 11:1.

A molar ratio of a sum of sulfur and selenium with respect to indium(Se+S/In) may be less than or equal to about 40:1, for example, lessthan or equal to about 30:1.

The cadmium free quantum dots may have a molar ratio of selenium withrespect to sulfur of greater than or equal to about 1:1, for example,greater than or equal to about 1.1:1. The cadmium free quantum dots mayhave a molar ratio of selenium with respect to sulfur of less than orequal to about 3:1, for example, less than or equal to about 2.8:1.

A sum of thicknesses of the first and second semiconductor nanocrystalshells may be greater than or equal to about 1.5 nm, for example,greater than or equal to about 2 nm.

In other embodiments, a method of producing the cadmium free quantum dotincludes:

reacting a zinc containing precursor and a selenium containing precursorin the presence of a semiconductor nanocrystal core particle includingindium and phosphorous in a heated organic solvent and an organic ligandat a first reaction temperature (e.g., for a time period of greater thanor equal to about 40 minutes) to form a first semiconductor nanocrystalshell on the semiconductor nanocrystal core; and

reacting a zinc containing precursor and a sulfur containing precursorin the presence of a particle having the first semiconductor nanocrystalshell formed on the core in the organic solvent and the organic ligandat a second reaction temperature to form a second semiconductornanocrystal shell on the first semiconductor nanocrystal shell, whereinthe organic ligand includes a carboxylic acid compound and a primaryamine compound.

During the formation of the first semiconductor nanocrystal shell, theorganic ligand may include the carboxylic acid compound and the primaryamine compound.

The method may not include lowering a temperature of a reaction mixtureincluding the particle having the first semiconductor nanocrystal shellon the core to a temperature below about 100° C., i.e., maintaining thetemperature of the reaction mixture at a temperature of greater than orequal to about 100° C.

In another embodiment, a quantum dot polymer composite includes apolymer matrix; and a plurality of quantum dots dispersed in the polymermatrix, wherein the plurality of quantum dots includes theaforementioned population of the cadmium free quantum dots.

The polymer matrix may include a crosslinked polymer, a binder polymerhaving a carboxylic acid group, or a combination thereof.

The crosslinked polymer may include a polymerization product of aphotopolymerizable monomer including at least carbon-carbon double bond,optionally a polymerization product of the photopolymerizable monomerand a multi-thiol compound having at least two thiol groups at itsterminal end, or a combination thereof.

The plurality of the quantum dots may not include cadmium.

The quantum dot polymer composite may include a plurality of fine metaloxide fine particles in the polymer matrix.

A blue light absorption rate of the quantum dot polymer composite withrespect to light having a wavelength of 450 nanometer may be greaterthan or equal to about 88% (for example when an amount of the cadmiumfree quantum dot is less than or equal to about 45% based on a totalweight of the composite).

The quantum dot polymer composite may be configured to have aphotoluminescent peak with a full width at half maximum of less than orequal to about 40 nm.

In another embodiment, a display device includes a light source and alight emitting element (e.g., photoluminescence element), wherein thelight emitting element includes the aforementioned quantum dot-polymercomposite and the light source is configured to provide the lightemitting element with incident light.

The incident light may have a luminescence peak wavelength of about 440nanometers to about 460 nanometers.

In an embodiment, the light emitting element may include a sheetincluding the quantum dot polymer composite.

The display device may further include a liquid crystal panel, and asheet of the quantum dot polymer composite may be disposed between thelight source and the liquid crystal panel.

In an embodiment, the display device includes as the light emittingelement a stacked structure including a substrate and a light emittinglayer disposed on the substrate, wherein the light emitting layerincludes a pattern of the quantum dot polymer composite and the patternincludes at least one repeating section configured to emit light at apredetermined wavelength.

The display device (e.g., the light emitting element) may be configuredto have a color reproducibility of greater than or equal to about 80%measured in accordance with a BT2020 standard.

The pattern may include a first section configured to emit first lightand a second section configured to emit second light having a differentcenter wavelength from the first light.

The light source may include a plurality of light-emitting unitscorresponding to each of the first section and the second section,wherein the light-emitting units may include a first electrode and asecond electrode facing each other and an electroluminescence layerdisposed between the first electrode and the second electrode.

The display device may further include a lower substrate, a polarizerdisposed under the lower substrate, and a liquid crystal layer disposedbetween the stacked structure and the lower substrate, wherein thestacked structure is disposed so that the light emitting layer faces theliquid crystal layer.

The display device may further include a polarizer between the liquidcrystal layer and the light emitting layer.

The light source may include an LED and optionally a light guide panel.

A population of cadmium free quantum dots of an embodiment may haveincreased solidity and improved size distribution. Thus, the populationof cadmium free quantum dots of the embodiment may exhibit a decreasedFWHM and a quantum dot polymer composite including the same may exhibitincreased excitation light absorption rate and enhanced light conversionrate. The cadmium free quantum dot of the embodiments may be used invarious display devices and biological labelling (e.g., bio sensor, bioimaging, etc.), a photo detector, a solar cell, a hybrid composite, andthe like. A display device including the population of cadmium freequantum dots of the embodiment may exhibit improved display quality(e.g., increased color reproducibility under a next generation colorstandard, BT2020)

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects will become apparent and more readilyappreciated from the following description of the embodiments, taken inconjunction with the accompanying drawings in which:

FIG. 1 is a view illustrating a photoluminescent peak and its full widthat half maximum of a single core and an ensemble thereof for a cadmiumbased quantum dot and cadmium free quantum dots;

FIG. 2 is a view illustrating the concept of solidity of a particle;

FIG. 3 is an exploded view of a display device according to anembodiment;

FIG. 4 is a view illustrating a process of producing a quantum dotpolymer composite pattern using a composition according to anembodiment;

FIG. 5A is a cross-sectional view of a device according to an exemplaryembodiment;

FIG. 5B is a cross-sectional view of a device according to anotherexemplary embodiment;

FIG. 6 is a cross-sectional view of a device according to yet anotherexemplary embodiment;

FIG. 7A is a transmission electron microscopic image of the populationof quantum dots prepared in Example 1;

FIG. 7B is a histogram showing a size distribution of the population ofquantum dots prepared in Example 1;

FIG. 8A is a transmission electron microscopic image of the populationof quantum dots prepared in Comparative Example 1;

FIG. 8B is a histogram showing a size distribution of the population ofquantum dots prepared in Comparative Example 1.

FIG. 9A is a transmission electron microscopic image of the populationof quantum dots prepared in Comparative Example 2;

FIG. 9B is a histogram showing a size distribution of the population ofquantum dots prepared in Comparative Example 2.

DETAILED DESCRIPTION

Advantages and characteristics of this disclosure, and a method forachieving the same, will become evident referring to the followingexample embodiments together with the drawings attached hereto. However,the embodiments should not be construed as being limited to theembodiments set forth herein. If not defined otherwise, all terms(including technical and scientific terms) in the specification may bedefined as commonly understood by one skilled in the art. The termsdefined in a generally-used dictionary may not be interpreted ideally orexaggeratedly unless clearly defined. In addition, unless explicitlydescribed to the contrary, the word “comprise” and variations such as“comprises” or “comprising”, will be understood to imply the inclusionof stated elements but not the exclusion of any other elements.

Further, the singular includes the plural unless mentioned otherwise.

In the drawings, the thickness of layers, films, panels, regions, etc.,are exaggerated for clarity. Like reference numerals designate likeelements throughout the specification.

It will be understood that when an element such as a layer, film,region, or substrate is referred to as being “on” another element, itcan be directly on the other element or intervening elements may also bepresent. In contrast, when an element is referred to as being “directlyon” another element, there are no intervening elements present.

“About” or “approximately” as used herein is inclusive of the statedvalue and means within an acceptable range of deviation for theparticular value as determined by one of ordinary skill in the art,considering the measurement in question and the error associated withmeasurement of the particular quantity (i.e., the limitations of themeasurement system). For example, “about” can mean within one or morestandard deviations, or within ±10% or 5% of the stated value.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this disclosure belongs. It willbe further understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art and thepresent disclosure, and will not be interpreted in an idealized oroverly formal sense unless expressly so defined herein.

Exemplary embodiments are described herein with reference to crosssection illustrations that are schematic illustrations of idealizedembodiments. As such, variations from the shapes of the illustrations asa result, for example, of manufacturing techniques and/or tolerances,are to be expected. Thus, embodiments described herein should not beconstrued as limited to the particular shapes of regions as illustratedherein but are to include deviations in shapes that result, for example,from manufacturing. For example, a region illustrated or described asflat may have rough and/or nonlinear features. Moreover, sharp anglesthat are illustrated may be rounded. Thus, the regions illustrated inthe figures are schematic in nature and their shapes are not intended toillustrate the precise shape of a region and are not intended to limitthe scope of the present claims.

It will be understood that, although the terms “first,” “second,”“third” etc. may be used herein to describe various elements,components, regions, layers and/or sections, these elements, components,regions, layers and/or sections should not be limited by these terms.These terms are only used to distinguish one element, component, region,layer or section from another element, component, region, layer, orsection. Thus, “a first element,” “component,” “region,” “layer” or“section” discussed below could be termed a second element, component,region, layer or section without departing from the teachings herein.

Furthermore, relative terms, such as “lower” or “bottom” and “upper” or“top,” may be used herein to describe one element's relationship toanother element as illustrated in the Figures. It will be understoodthat relative terms are intended to encompass different orientations ofthe device in addition to the orientation depicted in the Figures. Forexample, if the device in one of the figures is turned over, elementsdescribed as being on the “lower” side of other elements would then beoriented on “upper” sides of the other elements. The exemplary term“lower,” can therefore, encompasses both an orientation of “lower” and“upper,” depending on the particular orientation of the figure.Similarly, if the device in one of the figures is turned over, elementsdescribed as “below” or “beneath” other elements would then be oriented“above” the other elements. The exemplary terms “below” or “beneath”can, therefore, encompass both an orientation of above and below.

As used herein, unless a definition is otherwise provided, the term“substituted” refers to a compound or a group or a moiety wherein atleast one hydrogen atom thereof is substituted with a substituent. Thesubstituent may include a C1 to C30 alkyl group, a C2 to C30 alkenylgroup, a C2 to C30 alkynyl group, a C6 to C30 aryl group, a C7 to C30alkylaryl group, a C1 to C30 alkoxy group, a C1 to C30 heteroalkylgroup, a C3 to C30 heteroalkylaryl group, a C3 to C30 cycloalkyl group,a C3 to C15 cycloalkenyl group, a C6 to C30 cycloalkynyl group, a C2 toC30 heterocycloalkyl group, a halogen (—F, —Cl, —Br, or —I), a hydroxygroup (—OH), a nitro group (—NO₂), a cyano group (—CN), an amino group(—NRR′, wherein R and R′ are the same or different, and areindependently hydrogen or a C1 to C6 alkyl group), an azido group (—N₃),an amidino group (—C(═NH)NH₂), a hydrazino group (—NHNH₂), a hydrazonogroup (═N(NH₂)), a group represented by the formula ═N—R (wherein R ishydrogen or a C1 to C10 linear or branched alkyl group), an aldehydegroup (—C(═O)H), a carbamoyl group (—C(O)NH₂), a thiol group (—SH), anester group (—C(═O)OR, wherein R is a C1 to C6 alkyl group or a C6 toC12 aryl group), a carboxylic acid group (—COOH) or a salt thereof(—C(═O)OM, wherein M is an organic or inorganic cation), a sulfonic acidgroup (—SO₃H) or a salt thereof (—SO₃M, wherein M is an organic orinorganic cation), a phosphoric acid group (—PO₃H₂) or a salt thereof(˜PO₃MH or —PO₃M₂, wherein M is an organic or inorganic cation), or acombination thereof.

As used herein, unless a definition is otherwise provided, the term“hetero” means that the compound or group includes at least one (e.g.,one to three) heteroatom(s), wherein the heteroatom(s) is eachindependently N, O, S, Si, P, or a combination thereof.

As used herein, unless a definition is otherwise provided, the term“alkylene group” refers to a straight or branched chain, saturatedaliphatic hydrocarbon group having a valence of at least two. Thealkylene group may be optionally substituted with one or moresubstituents.

As used herein, unless a definition is otherwise provided, the term“arylene group” refers to a functional group having a valence of atleast two and formed by the removal of at least two hydrogen atoms fromone or more rings of an aromatic hydrocarbon, wherein the hydrogen atomsmay be removed from the same or different rings (preferably differentrings), each of which rings may be aromatic or nonaromatic. The arylenegroup may be optionally substituted with one or more substituents.

As used herein, unless a definition is otherwise provided, the term“aliphatic hydrocarbon group” refers to a C1 to C30 linear or branchedalkyl group, C2 to C30 linear or branched alkenyl group, and C2 to C30linear or branched alkynyl group, the term “aromatic hydrocarbon group”refers to a C6 to C30 aryl group or a C2 to C30 heteroaryl group, andthe term “alicyclic hydrocarbon group” refers to a C3 to C30 cycloalkylgroup, a C3 to C30 cycloalkenyl group, and a C3 to C30 cycloalkynylgroup.

As used herein, unless a definition is otherwise provided, the term“(meth)acrylate” refers to acrylate and/or methacrylate. The(meth)acrylate may include a (C1 to C10 alkyl)acrylate and/or a (C1 toC10 alkyl)methacrylate.

In some embodiment, “hydrophobic moiety” may be a moiety that may causea compound including the same to agglomerate in an aqueous (hydrophilic)solution and to have a tendency to repel water. For example, thehydrophobic moiety may include an aliphatic hydrocarbon group (e.g.,alkyl, alkenyl, alkynyl, etc.) having at least one (e.g., at least two,three, four, five, or six, or higher) carbon atoms, an aromatichydrocarbon group having at least six carbon atoms (e.g., phenyl,naphthyl, arylalkyl group, etc.), or an alicyclic hydrocarbon grouphaving at least five carbon atoms (e.g., cyclohexyl, norbornenyl, etc.).

As used herein, unless a definition is otherwise provided, the term“dispersion” refers to a system in which a dispersed phase is a solidand a continuous phase includes a liquid. For example, the term“dispersion” may refer to a colloidal dispersion, wherein the dispersedphase includes particles having a dimension of at least about 1nanometer (nm) (e.g., at least about 2 nm, at least about 3 nm, or atleast about 4 nm) and less than or equal to about several micrometers(μm) (e.g., 1 μm or less, 2 μm or less).

As used herein, the term “a population of quantum dot” and the term“quantum dot population” are interchangeable.

As used herein, unless a definition is otherwise provided, the term“Group” in the term Group III, Group II, and the like refers to a groupof the Periodic Table of Elements.

As used herein, “Group I” refers to Group IA and Group IB, and mayinclude Li, Na, K, Rb, and Cs but are not limited thereto.

As used herein, “Group II” refers to Group IIA and a Group IIB, andexamples of the Group II metal may include Cd, Zn, Hg, and Mg, but arenot limited thereto.

As used herein, “Group III” refers to Group IIIA and Group IIIB, andexamples of the Group III metal may include Al, In, Ga, and TI, but arenot limited thereto.

As used herein, “Group IV” refers to Group IVA and Group IVB, andexamples of the Group IV metal may include Si, Ge, and Sn but are notlimited thereto. As used herein, the term “a metal” may include asemi-metal such as Si.

As used herein, “Group V” refers to Group VA and may include nitrogen,phosphorus, arsenic, antimony, and bismuth but is not limited thereto.

As used herein, “Group VI” refers to Group VIA and may include sulfur,selenium, and tellurium, but is not limited thereto.

A semiconductor nanocrystal particle (also referred to as a quantum dot)is a nano-sized crystalline material. The semiconductor nanocrystalparticle may have a large surface area per unit volume due to its verysmall size and may exhibit different characteristics from bulk materialshaving the same composition due to a quantum confinement effect. Quantumdots may absorb light from an excitation source to be excited, and mayemit energy corresponding to an energy bandgap of the quantum dots.

The quantum dots have a potential applicability in various devices(e.g., an electronic device) due to their unique photoluminescencecharacteristics. Quantum dots having properties currently applicable toan electronic device are mostly cadmium-based. However, cadmium maycause a serious environment/health problem and thus is a restrictedelement. As a type of cadmium free quantum dot, a Group III-V-basednanocrystal has been extensively researched. However, cadmium freequantum dots have technological drawbacks in comparison with the cadmiumbased ones.

For example, for their application in a device, quantum dots often useblue light (e.g., having a wavelength of about 450 nm) as excitationenergy source. The cadmium based quantum dots generally have a highlevel of blue light absorption rate. However, in the case of currentlyavailable cadmium free quantum dots, the absorption strength for bluelight (e.g., having a wavelength of about 450 nm) is not high, and thismay lead to a decreased brightness. To be applicable to a device,quantum dots may be dispersed in a host matrix (e.g., including apolymer and/or inorganics) to form a composite. Such a quantum dotcomposite and/or a color filter including the same may provide a displaythat may show high brightness, wide viewing angle, and high colorreproducibility. However, a weight of the quantum dots that may beincluded in the composite may be restricted due to variousprocess-related problems. Thus, it is desirable to develop a cadmiumfree quantum dot having enhanced blue absorption rate and improvedbrightness at a given weight. It would be a further advantage if thequantum dot exhibited thermal stability.

Quantum dots based on a Group III-V compound including indium andphosphorous have a smaller energy bandgap and their Bohr radiuses arelarger than those of the cadmium based quantum dots, which results in agreater change in a FWHM depending on their size. In the InP basedquantum dots, the indium and the phosphorous have a high tendency toforming a covalent bond, which makes it difficult to form a uniformpopulation of the nanoparticles in comparison with the cadmium basedquantum dots, and thus has a substantial and adverse effect on thephotoluminescent properties (e.g., the FWHM) of the resulting quantumdot. Referring to FIG. 1, in the case of the cadmium based quantum dot(e.g., a CdSe core), luminous properties of a single particle are notsignificantly different from those of ensembles (pluralities) thereof.In contrast, in the case of a quantum dot based on the indium phosphide(e.g., an InP core), properties of a single particle are significantlydifferent from those of ensembles thereof. For example, in case of theInP core, a single particle exhibits a narrow FWHM while an ensemblethereof exhibits a greatly increased FWHM.

Moreover, a cadmium free quantum dot tends to have poor uniformity in asize of the core, and forming a shell (e.g., a ZnSe or ZnS shell) on thecore may further aggravate its uniformity problem, such thatnon-uniformity may significantly increase. In order to enhance stabilitythereof, a ZnS shell may be provided as the outermost shell of thequantum dot, but a large difference in the lattice constant between theInP core and ZnS shell may make it more difficult to provide a uniformcoating and thereby a core-shell type indium phosphide based quantum dottends to have a wider particle size distribution. Therefore, in the caseof the core-shell type quantum dot based on the indium phosphideprepared in a currently available method, a standard deviation of theparticle size of the quantum dots is generally greater than 20% of theaverage particle size.

When the quantum dot has a thin shell, the uniformity of the particlesize distribution may be controlled at a certain level. However, in caseof the cadmium free quantum dot, a substantial increase in a shellthickness may be desired in order to secure quantum dot properties(e.g., quantum efficiency and stability). At the increased shellthickness, it is difficult for the quantum dots to have a desired levelof uniformity in a particle size distribution and thus the standarddeviation with respect to their average particle size tend to be greaterthan 20%.

In addition, the fact that a population of quantum dots has a widerparticle size distribution and an increased FWHM may also suggest thatthe number of small particles not having a desired thickness of shelland the number of large particles having excessively increased thicknessof shell may simultaneously increase. When such a population of quantumdots is processed into a composite, a desired level of stability cannotbe assured and/or the number of the quantum dots per a given weight inthe composite may decrease and thus desired optical properties (e.g., ablue light absorption rate and luminous efficiency) may not be obtained.

In an embodiment, a population of quantum dots includes a plurality ofcadmium free quantum dots. The population of quantum dots may notinclude cadmium, i.e., may be free of cadmium or have no cadmium added.A cadmium free quantum dot (hereinafter, also referred to as “quantumdot”) of an embodiment has a core-multishell structure. In themulti-shell structure, adjacent shells have different compositions fromeach other. The cadmium free quantum dots of an embodiment include asemiconductor nanocrystal core including indium and phosphorous, a firstsemiconductor nanocrystal shell disposed on the semiconductornanocrystal core and including zinc and selenium, and a secondsemiconductor nanocrystal shell disposed on the first semiconductornanocrystal shell and including zinc and sulfur, and not includingcadmium. The first semiconductor nanocrystal shell may have acomposition different from the second semiconductor nanocrystal shell.

An average particle size of the population of the cadmium free quantumdots of an embodiment may be greater than or equal to about 5.5 nm, forexample, 5.6 nm or greater, greater than or equal to about 5.7 nm,greater than or equal to about 5.8 nm, greater than or equal to about5.9 nm, greater than or equal to about 6.0 nm, greater than or equal toabout 6.1 nm, greater than or equal to about 6.2 nm, greater than orequal to about 6.3 nm, greater than or equal to about 6.4 nm, greaterthan or equal to about 6.5 nm, greater than or equal to about 7.0 nm,greater than or equal to about 7.5 nm, greater than or equal to about7.6 nm, greater than or equal to about 7.7 nm, greater than or equal toabout 7.8 nm, greater than or equal to about 7.9 nm, or greater than orequal to about 8.0 nm. An average particle size of the population of thecadmium free quantum dots of an embodiment may be less than or equal toabout 20 nm, for example, less than or equal to about 19 nm, less thanor equal to about 18 nm, less than or equal to about 17 nm, less than orequal to about 16 nm, less than or equal to about 15 nm, less than orequal to about 14 nm, less than or equal to about 13 nm, less than orequal to about 12 nm, less than or equal to about 11 nm, less than orequal to about 10 nm, or less than or equal to about 9 nm. The particlesize may be a diameter. (For example, when the particle is notsubstantially a sphere shape the particle size may be a diameter that iscalculated by converting a two dimensional area determined in atransmission electron microscopic image into a circle).

A standard deviation of the particle sizes of the population of thecadmium free quantum dots may be less than or equal to about 20% of theaverage particle size. An average solidity of the population of thecadmium free quantum dots is greater than or equal to about 0.85.

As used herein, the term “solidity” refers to a ratio of an area (B) ofa two dimensional area of a quantum dot with respect to an area A of aconvex hull. The convex hull may be defined as the smallest convex setof points in which a set of all points constituting a two dimensionalimage of a given quantum dot obtained by an electron microscopicanalysis is contained. (see FIG. 2) The solidity may be measured by atransmission electron scopic analysis. For example, a computer program(e.g., an image processing program such as “image J”) may be used tocalculate (an average value of) solidity from a TEM image of the quantumdots.

Efficient passivation of the core may require an increased thickness ofcoating, but the increase in the coating thickness may make the sizedistribution of the population of the particles wider and may cause adecrease in the solidity of each of the particles. Thus, when apopulation of indium phosphide based core-shell quantum dots is preparedin the conventional manner to have an average size of greater than orequal to about 5.5 nm (e.g., greater than or equal to about 5.6 nm), thesize distribution has a standard deviation of greater than or equal toabout 24% (e.g., greater than or equal to about 25%) and the averagesolidity thereof may be less than or equal to about 0.83 (e.g., lessthan or equal to about 0.80).

However, when being prepared in the method that will desired below, thepopulation of the cadmium free quantum dots may have an average particlesize of greater than or equal to about 5.5 nm, for example, greater thanor equal to about 5.6 nm, greater than or equal to about 5.7 nm, greaterthan or equal to about 5.8 nm, greater than or equal to about 5.9 nm, orgreater than or equal to about 6 nm and at the same time, a standarddeviation of the population of the cadmium free quantum dots may be lessthan or equal to about 20%, for example, less than or equal to about19%, less than or equal to about 18%, less than or equal to about 17%,less than or equal to about 16%, less than or equal to about 15%, orless than or equal to about 14% and an average solidity of thepopulation of the cadmium free quantum dots may be greater than or equalto about 0.85, for example, greater than or equal to about 0.86, greaterthan or equal to about 0.87, greater than or equal to about 0.88,greater than or equal to about 0.89, or greater than or equal to about0.9.

A population of the quantum dots having the aforementioned solidity andthe particle size distribution may exhibit an improved level of a fullwidth at half maximum. For example, a quantum dot population of anembodiment may have a FWHM of less than or equal to about 40 nm, forexample, less than or equal to about 39 nm, less than or equal to about38 nm, or less than or equal to about 37 nm.

In the cadmium free quantum dots, the size of the core may be selectedin view of a desired photoluminescent wavelength. For example, a size ofthe core may be greater than or equal to about 2 nm, greater than orequal to about 2.1 nm, greater than or equal to about 2.3 nm, greaterthan or equal to about 2.4 nm, greater than or equal to about 2.5 nm,greater than or equal to about 2.6 nm, greater than or equal to about2.7 nm, greater than or equal to about 2.8 nm, greater than or equal toabout 2.9 nm. For example, a size of the core may be less than or equalto about 4.5 nm, for example, less than or equal to about 4 nm, or lessthan or equal to about 3.5 nm. The core may include indium andphosphorous. The core may further include zinc.

The shell is a multi-layered shell. The shell may include a firstsemiconductor nanocrystal shell including zinc and selenium. The shellmay include a second semiconductor nanocrystal shell disposed on or overthe first semiconductor nanocrystal shell and including zinc and sulfur.

The first semiconductor nanocrystal shell may include (e.g., consistessentially, of, or consist of) ZnSe. The first semiconductornanocrystal shell may not include sulfur (S), i.e., may be free of S orhave no S added. In an embodiment, the first semiconductor nanocrystalshell may not include, i.e., may be free of ZnSeS. In other embodiments,the first semiconductor nanocrystal shell may include ZnSe, ZnSeS, or acombination thereof. The first semiconductor nanocrystal shell (e.g.,consisting of ZnSe) may be disposed directly on the semiconductornanocrystal core. The first semiconductor nanocrystal shell may have athickness of greater than or equal to about 3 monolayer (ML), or greaterthan or equal to about 4 ML. A thickness of the first semiconductornanocrystal shell may be less than or equal to about 10 ML, for example,less than or equal to about 9 ML, less than or equal to about 8 ML, lessthan or equal to about 7 ML, less than or equal to about 6 ML, less thanor equal to about 5 ML, or less than or equal to about 4 ML.

The second semiconductor nanocrystal shell includes Zn and S. The secondsemiconductor nanocrystal shell may be disposed directly on the firstsemiconductor nanocrystal shell. The second semiconductor nanocrystalshell may have a composition varying in a radial direction. In anembodiment, the second semiconductor nanocrystal shell may include ZnS,ZnSeS, or a combination thereof. The second semiconductor nanocrystalshell may include at least two layers, and adjacent layers may havedifferent composition from each other. In an embodiment, the secondsemiconductor nanocrystal shell may include the outermost layerconsisting of ZnS.

In the cadmium free quantum dots of the embodiments, a molar ratio ofzinc with respect to indium may be greater than or equal to about 10:1,for example, greater than or equal to about 11:1, greater than or equalto about 12:1, greater than or equal to about 13:1, greater than orequal to about 14:1, greater than or equal to about 15:1, greater thanor equal to about 16:1, greater than or equal to about 17:1, greaterthan or equal to about 18:1, greater than or equal to about 19:1,greater than or equal to about 20:1, greater than or equal to about21:1, greater than or equal to about 22:1, greater than or equal toabout 23:1, greater than or equal to about 24:1, or greater than orequal to about 25:1. In the cadmium free quantum dots of theembodiments, a molar ratio of zinc with respect to indium may be lessthan or equal to about 60:1, for example, less than or equal to about55:1, less than or equal to about 50:1, less than or equal to about45:1, less than or equal to about 40:1, less than or equal to about35:1, less than or equal to about 34:1, less than or equal to about33:1, less than or equal to about 32:1, less than or equal to about31:1, less than or equal to about 30:1, less than or equal to about29:1, less than or equal to about 28:1, or less than or equal to about27:1.

In the cadmium free quantum dots of the embodiments, a molar ratio ofselenium with respect to indium may be greater than or equal to about5.7:1, for example, greater than or equal to about 5.8:1, greater thanor equal to about 5.9:1, greater than or equal to about 6.0:1, greaterthan or equal to about 6.1:1, greater than or equal to about 6.2:1,greater than or equal to about 6.3:1, greater than or equal to about6.4:1, greater than or equal to about 6.5:1, greater than or equal toabout 6.6:1, greater than or equal to about 6.7:1, greater than or equalto about 6.8:1, greater than or equal to about 6.9:1, greater than orequal to about 7.0:1, greater than or equal to about 8:1, greater thanor equal to about 9:1, greater than or equal to about 10:1, greater thanor equal to about 11:1, greater than or equal to about 12:1, or greaterthan or equal to about 13:1. In the cadmium free quantum dots of theembodiments, a molar ratio of selenium with respect to indium may beless than or equal to about 30:1, less than or equal to about 29:1, lessthan or equal to about 28:1, less than or equal to about 27:1, less thanor equal to about 26:1, less than or equal to about 25:1, less than orequal to about 24:1, less than or equal to about 23:1, less than orequal to about 22:1, less than or equal to about 21:1, less than orequal to about 20:1, less than or equal to about 19:1, less than orequal to about 18:1, less than or equal to about 17:1, less than orequal to about 16:1, less than or equal to about 15:1, less than orequal to about 14:1, less than or equal to about 13:1, less than orequal to about 12:1, less than or equal to about 11:1, or less than orequal to about 10:1.

In the cadmium free quantum dots of the embodiments, a molar ratio ofsulfur with respect to indium may be greater than or equal to about 2:1,for example, greater than or equal to about 3:1, greater than or equalto about 3.1:1, greater than or equal to about 3.2:1, greater than orequal to about 3.4:1, greater than or equal to about 4:1, or greaterthan or equal to about 5:1. In the cadmium free quantum dots of theembodiments, a molar ratio of sulfur with respect to indium may be lessthan or equal to about 20:1, for example, less than or equal to about19:1, less than or equal to about 18:1, less than or equal to about17:1, less than or equal to about 16:1, less than or equal to about15:1, less than or equal to about 14:1, less than or equal to about13:1, less than or equal to about 12:1, less than or equal to about11:1, less than or equal to about 10:1, or less than or equal to about9:1.

In the cadmium free quantum dots of the embodiments, a molar ratio ofselenium with respect to sulfur may be greater than or equal to about0.87:1, for example, greater than or equal to about 0.88:1, greater thanor equal to about 0.89:1, greater than or equal to about 0.9:1, greaterthan or equal to about 1, greater than or equal to about 1.1:1, greaterthan or equal to about 1.2:1, greater than or equal to about 1.3:1,greater than or equal to about 1.4:1, greater than or equal to about1.5:1, greater than or equal to about 1.6:1, or greater than or equal toabout 1.7:1. In the cadmium free quantum dots of the embodiments, amolar ratio of selenium with respect to sulfur may be less than or equalto about 5:1, for example, less than or equal to about 4:1, less than orequal to about 3.5:1, less than or equal to about 3:1, less than orequal to about 2.5:1, or less than or equal to about 2:1.

In the cadmium free quantum dots of the embodiments, a molar ratio ofthe sum of selenium and sulfur with respect to indium [(S+Se)/In] may begreater than or equal to about 3:1, for example, greater than or equalto about 4:1, greater than or equal to about 5:1, greater than or equalto about 6, greater than or equal to about 7, greater than or equal toabout 8, greater than or equal to about 9:1, greater than or equal toabout 10:1, greater than or equal to about 11:1, greater than or equalto about 12:1, greater than or equal to about 13:1, greater than orequal to about 14:1, greater than or equal to about 15:1, greater thanor equal to about 16:1, greater than or equal to about 17:1, greaterthan or equal to about 18:1, greater than or equal to about 19:1,greater than or equal to about 20:1, or greater than or equal to about21:1. In the cadmium free quantum dots of the embodiments, a molar ratioof the sum of selenium and sulfur with respect to indium [(S+Se)/In] maybe less than or equal to about 40:1, less than or equal to about 35:1,less than or equal to about 30:1, less than or equal to about 25:1, lessthan or equal to about 24:1, less than or equal to about 23:1, less thanor equal to about 22:1, less than or equal to about 21:1, less than orequal to about 20:1, less than or equal to about 19:1, or less than orequal to about 18:1.

In the cadmium free quantum dots of the embodiments, a molar ratio ofzinc with respect to the sum of selenium and sulfur [Zn/(S+Se)] may begreater than or equal to about 1:1 and less than or equal to about1.5:1.

In an embodiment, the cadmium free quantum dot may not include boron,i.e., may be free of boron or have no boron added.

A display device based on the quantum dot may provide an improveddisplay quality in terms of color purity, brightness, and the like. Forexample, a conventional liquid crystal display device (e.g., aconventional LCD device) is a device realizing color by polarized lightthat passes through a liquid crystal layer and a color filter, and has aproblem of narrow viewing angle and lower brightness due to the lowlight transmittance of the absorptive color filter. The quantum dot hasa theoretical quantum yield of about 100% and may emit light of highcolor purity (e.g., having a FWHM of less than or equal to about 40 nm),thereby realizing enhanced luminance efficiency and improved colorpurity. Thus, replacing the absorptive color filter with aphotoluminescent type color filter including quantum dots may contributea wider viewing angle and an increased brightness.

In order to be utilized in a device, however, the quantum dot may beprocessed into a form of a composite wherein a plurality of the quantumdots are dispersed in a host matrix (e.g., including a polymer and/orinorganic material). A quantum dot polymer composite or a color filterincluding the same may provide a display device having high brightness,wide viewing angle, and high color purity. The population of the cadmiumfree quantum dots may exhibit a relatively narrow FWHM and thus makes itpossible to realize enhanced color purity even under a next generationcolor standard such as BT2020.

The cadmium free quantum dots may include an organic ligand. The organicligand may bound to a surface of the quantum dot. The organic ligand mayinclude a carboxylic acid compound and a primary amine compound. Acarboxylic acid group of the carboxylic acid compound may include a C5to C30 hydrocarbon group, and a primary amine group of the primary aminecompound may include a C5 to C30 hydrocarbon group. The primary aminegroup may include a C5 to C30 alkenyl group.

The carboxylic acid compound may be represented by Chemical Formula 1and the primary amine compound may be represented by Chemical Formula 2:R¹COOH  Chemical Formula 1R²NH₂  Chemical Formula 2

wherein R¹ and R² are the same or different and each independently asubstituted or unsubstituted aliphatic hydrocarbon group (e.g., alkyl,alkenyl, or alkynyl) having a carbon number of greater than or equal toabout 5 and less than or equal to about 40 or less than or equal toabout 30, for example a substituted or unsubstituted C5 to C30 alkyl,alkenyl, or alkynyl group, a substituted or unsubstituted C5 to C30alicyclic hydrocarbon group, a substituted or unsubstituted C6 to C30aromatic hydrocarbon group (e.g., aryl), or a combination thereof.

The carboxylic acid compound may include pentanoic acid, hexanoic acid,heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, undecanoicacid, dodecanoic acid, tridecanoic acid, tetradecanoic acid,pentadecanoic acid, hexadecanoic acid, heptadecanoic acid, octadecanoicacid, nonadecanoic acid, eicosanoic acid, heneicosanoic acid, docosanoicacid, tricosanoic acid, tetracosanoic acid, pentacosanoic acid,hexacosanoic acid, heptacosanoic acid, octacosanoic acid, nonacosanoicacid, triacontanoic acid, tetra-triacontanoic acid, pentatriacontanoicacid, hexatriacontanoic acid, alpha linolenic acid, eicosapentaenoicacid, docosahexaenoic acid, linolenic acid, gamma-linolenic acid,dihomo-gamma-linolenic acid, arachidonic acid, paullinic acid, oleicacid, elaidic acid, eicosenoic acid, erucic acid, nervonic acid, or acombination thereof.

The primary amine compound may include a pentylamine, hexylamine,heptylamine, octylamine, nonylamine, decylamine, undecylamine,dodecylamine, tridecylamine, pentadecylamine, hexadecylamine,heptadecylamine, ocatdecylamine, nonadecylamine, oleylamine, or acombination thereof.

The quantum dot may emit green light. The green light may have a maximumpeak wavelength of greater than or equal to about 500 nm, for example,greater than or equal to about 510 nm, and less than or equal to about600 nm, for example less than or equal to about 560 nm. The quantum dotmay emit red light. The red light may have a maximum peak wavelength ofgreater than or equal to about 600 nm, for example, greater than orequal to about 610 nm, and less than or equal to about 650 nm, forexample less than or equal to about 640 nm.

The cadmium free quantum dot may have a quantum yield of greater than orequal to about 80%, greater than or equal to about 81%, or greater thanor equal to about 82%. The cadmium free quantum dot may have a FWHM ofless than or equal to about 45 nm, for example, less than or equal toabout 44 nm, less than or equal to about 43 nm, less than or equal toabout 42 nm, or less than or equal to about 41 nm.

In the UV-Vis absorption spectrum of the cadmium free quantum dot, thefirst absorption peak may be present in a wavelength range of greaterthan or equal to about 450 nm and less than a photoluminescent peakwavelength of the cadmium free quantum dot. In an embodiment, a greenlight emitting quantum dot may have the first absorption peak wavelengththat is for example, greater than or equal to about 480 nm, greater thanor equal to about 485 nm, or greater than or equal to about 490 nm andless than or equal to about 520 nm, less than or equal to about 515 nm,or less than or equal to about 510 nm. In an embodiment, a red lightemitting quantum dot may have the first absorption peak wavelength thatis for example, greater than or equal to about 580 nm, greater than orequal to about 590 nm and less than or equal to about 620 nm, less thanor equal to about 610 nm.

Another embodiment is directed to a method of producing theaforementioned population of the cadmium free quantum dots, whichincludes:

reacting a zinc containing precursor and a selenium containing precursorin the presence of a semiconductor nanocrystal core particle includingindium and phosphorous in a heated organic solvent and an organic ligandat a first reaction temperature for a time period of greater than orequal to about 40 minutes to form a first semiconductor nanocrystalshell on the semiconductor nanocrystal core; and

reacting a zinc containing precursor and a sulfur containing precursorin the presence of a particle having the first semiconductor nanocrystalshell formed on the core in the organic solvent and the organic ligandat a second reaction temperature to form a second semiconductornanocrystal shell on the first semiconductor nanocrystal shell, whereinthe organic ligand includes a carboxylic acid compound and a primaryamine compound.

During the formation of the first semiconductor nanocrystal shell, theorganic ligand may include the carboxylic acid compound and the primaryamine compound.

In the aforementioned method, the amounts of the selenium containingprecursor, the sulfur containing precursor, and the zinc containingprecursor may be controlled so that the resulting quantum dots may havethe molar ratios of the selenium and sulfur with respect to indium (orzinc) within the aforementioned ranges.

Details of the cadmium free quantum dots (e.g., their structure and thecomposition), the carboxylic acid compound, the primary amine compound,and the like are the same as set forth above.

In the reaction system, the amount of the carboxylic acid compound andthe amount of the primary amine compound may be controlled with respectto the zinc containing precursor.

The carboxylic acid compound may be present in an amount greater than orequal to about 0.5 moles, greater than or equal to about 0.6 moles,greater than or equal to about 0.7 moles, greater than or equal to about0.8 moles, greater than or equal to about 0.9 moles, greater than orequal to about 1 moles, greater than or equal to about 2 moles, greaterthan or equal to about 3 moles, and less than or equal to about 10moles, for example, less than or equal to about 5 moles, and less thanor equal to about 4 moles, per one mole of the zinc containingprecursor. The primary amine compound may be present in an amountgreater than or equal to about 0.5 moles, greater than or equal to about0.6 moles, greater than or equal to about 0.7 moles, greater than orequal to about 0.8 moles, greater than or equal to about 0.9 moles,greater than or equal to about 1 moles, greater than or equal to about 2moles, greater than or equal to about 3 moles, and less than or equal toabout 10 moles, for example, less than or equal to about 5 moles, andless than or equal to about 4 moles, per one mole of the zinc containingprecursor.

In an embodiment, the organic ligand may further include an additionalorganic ligand compound such as R₂NH, R₃N, RSH, RH₂PO, R₂HPO, R₃PO,RH₂P, R₂HP, R₃P, ROH, RCOOR′, RPO(OH)₂, RHPOOH, R₂POOH, (wherein R andR′ are the same or different, and are independently a hydrogen, C1 toC40 aliphatic hydrocarbon group, such as C1 to C40 (C3 to C24) alkyl orC2 to C40 (e.g., C3 to C24) alkenyl group, C2 to C40 (e.g., C3 to C24)alkynyl group or a C6 to C40 aromatic hydrocarbon group such as a C6 toC20 aryl group), a polymeric organic ligand, or a combination thereof.

Examples of the additional organic ligand compound may include:

a thiol compound such as methane thiol, ethane thiol, propane thiol,butane thiol, pentane thiol, hexane thiol, octane thiol, dodecane thiol,hexadecane thiol, octadecane thiol, benzyl thiol;

an amine compound such as dimethylamine, diethylamine, dipropylamine,tributylamine, trioctylamine, or a combination thereof;

a phosphine compound such as methyl phosphine, ethyl phosphine, propylphosphine, butyl phosphine, pentyl phosphine, octyl phosphine, dioctylphosphine, tributyl phosphine, trioctyl phosphine, or a combinationthereof;

a phosphine oxide compound such as methyl phosphine oxide, ethylphosphine oxide, propyl phosphine oxide, butyl phosphine oxide, pentylphosphine oxide, tributyl phosphine oxide, octylphosphine oxide, dioctylphosphine oxide, trioctyl phosphine oxide, or a combination thereof;

diphenyl phosphine, triphenyl phosphine, or an oxide compound thereof,or a combination thereof;

a mono- or di(C5 to C20 alkyl)phosphinic acid such as mono- ordihexylphosphinic acid, mono- or dioctylphosphinic acid, mono- ordidodecylphosphinic acid, mono- or di(tetradecyl)phosphinic acid, mono-or di(hexadecyl)phosphinic acid, mono- or di(octadecyl)phosphinic acid,or a combination thereof;

a C5 to C20 alkylphosphonic acid such as hexylphosphonic acid,octylphosphonic acid, dodecylphosphonic acid, tetradecylphosphonic acid,hexadecylphosphonic acid, octadecylphosphonic acid, or a combinationthereof;

or a combination thereof.

Examples of the organic solvent may include a C6 to C22 secondary aminesuch as dioctylamine, a C6 to C40 tertiary amine such as a trioctylamine (TOA), a nitrogen-containing heterocyclic compound such aspyridine, a C6 to C40 olefin such as octadecene, a C6 to C40 aliphatichydrocarbon such as hexadecane, octadecane, squalene, or squalane, anaromatic hydrocarbon substituted with a C6 to C30 alkyl group such asphenyldodecane, phenyltetradecane, or phenyl hexadecane, a primary,secondary, or tertiary phosphine (e.g., trioctyl phosphine) containingat least one (e.g., 1, 2, or 3) C6 to C22 alkyl group, a phosphine oxide(e.g., trioctylphosphine oxide) containing at least one (e.g., 1, 2, or3) C6 to C22 alkyl group, a C12 to C22 aromatic ether such as a phenylether or a benzyl ether, or a combination thereof. The organic solventmay include a tertiary amine (e.g., trioctyl amine).

The organic solvent (e.g., including the zinc containing precursor andan organic ligand such as a carboxylic acid compound) may be heated to apredetermined temperature (e.g., of greater than or equal to about 100°C., for example, greater than or equal to about 120° C., greater than orequal to about 150° C., greater than or equal to about 200° C., greaterthan or equal to about 250° C., or greater than or equal to about 270°C.) and less than or equal to about the first reaction temperature undervacuum and/or an inert atmosphere. The heated organic solvent (e.g.,including the zinc containing precursor and an organic ligand such as acarboxylic acid compound) may further include the primary aminecompound.

Details of the semiconductor nanocrystal core including the indium andthe phosphorous are the same as set forth above. The core may becommercially available or may be prepared in any appropriate method. Thepreparation of the core is not particularly limited and may be performedin any method of producing an indium phosphide based core. In someembodiment, the core may be synthesized in a hot injection mannerwherein a solution including a metal precursor (e.g., an indiumprecursor) and optionally a ligand is heated at a high temperature(e.g., of greater than or equal to about 200° C.) and then a phosphorousprecursor is injected the heated hot solution. In other embodiments, thesynthesis of the core may adopt a low temperature injection method. Theprepared core may be injected the heated organic solvent at atemperature of greater than or equal to about 100° C.

Types of the zinc containing precursor are not particularly limited andselected appropriately. In an embodiment, the zinc containing precursormay include a Zn metal powder, an alkylated Zn compound, Zn alkoxide, Zncarboxylate, Zn nitrate, Zn perchlorate, Zn sulfate, Zn acetylacetonate,Zn halide, Zn cyanide, Zn hydroxide, Zn oxide, Zn peroxide, Zncarbonate, or a combination thereof. Examples of the zinc containingprecursor may include dimethyl zinc, diethyl zinc, zinc acetate, zincacetylacetonate, zinc iodide, zinc bromide, zinc chloride, zincfluoride, zinc carbonate, zinc cyanide, zinc nitrate, zinc oxide, zincperoxide, zinc perchlorate, zinc sulfate, and the like. The zinccontaining precursor may be used alone or in a combination of two ormore compounds.

Types of the selenium containing precursor are not particularly limitedand may be selected appropriately. For example, the selenium containingprecursor may include selenium-trioctylphosphine (Se-TOP),selenium-tributylphosphine (Se-TBP), selenium-triphenylphosphine(Se-TPP), or a combination thereof, but is not limited thereto.

The first reaction temperature may be selected appropriately and, forexample, may be greater than or equal to about 280° C., greater than orequal to about 290° C., greater than or equal to about 300° C., greaterthan or equal to about 310° C., or greater than or equal to about 315°C. and less than or equal to about 390° C., less than or equal to about380° C., less than or equal to about 370° C., less than or equal toabout 360° C., less than or equal to about 350° C., less than or equalto about 340° C., less than or equal to about 330° C.

After or during the heating to the first reaction temperature, aselenium containing precursor may be injected at least one time (e.g.,at least twice, at least third times).

The reaction time at the first reaction temperature may be greater thanor equal to about 40 minutes, for example, greater than or equal toabout 50 minutes, greater than or equal to about 60 minutes, greaterthan or equal to about 70 minutes, greater than or equal to about 80minutes, greater than or equal to about 90 minutes, and less than orequal to about 4 hours, for example, less than or equal to about 3hours, less than or equal to about 2 hours.

By the reaction at the first reaction temperature for the aforementionedtime period, the first semiconductor nanocrystal shell having athickness of greater than or equal to about 3 ML may be formed.

In this case, the amount of the selenium containing precursor withrespect to the indium may be controlled such that during thepredetermined reaction time, the first semiconductor nanocrystal shellhaving the predetermined thickness may be formed. In an embodiment, theamount of the selenium per one mole of indium may be greater than orequal to about 7 moles, greater than or equal to about 8 moles, greaterthan or equal to about 9 moles, or greater than or equal to about 10moles, but is not limited there to. In an embodiment, the amount of theselenium per one mole of indium may be less than or equal to about 40moles, less than or equal to about 30 moles, less than or equal to about25 moles, less than or equal to about 20 moles, less than or equal toabout 18 moles, or less than or equal to about 15 moles, but is notlimited thereto.

The method may not include lowering a temperature of a reaction mixtureincluding the particle having the first semiconductor nanocrystal shellon the core to a temperature of below 100° C., for example, less than orequal to about 50° C., less than or equal to about 30° C., or at roomtemperature. In other words, the method may include maintaining atemperature of a reaction mixture including the particle having thefirst semiconductor nanocrystal shell on the core at a temperature ofgreater than or equal to 100° C., for example, greater than or equal to50° C., greater than or equal to 30° C.

Types of the sulfur containing precursor are not particularly limitedand may be selected appropriately. The sulfur containing precursor mayinclude hexane thiol, octane thiol, decane thiol, dodecane thiol,hexadecane thiol, mercapto propyl silane, sulfur-trioctylphosphine(S-TOP), sulfur-tributylphosphine (S-TBP), sulfur-triphenylphosphine(S-TPP), sulfur-trioctylamine (S-TOA), trimethylsilyl sulfide, ammoniumsulfide, sodium sulfide, or a combination thereof. The sulfur containingprecursor may be injected at least on time (e.g., at least twice).

The second reaction temperature may be selected appropriately and, forexample, may be greater than or equal to about 280° C., greater than orequal to about 290° C., greater than or equal to about 300° C., greaterthan or equal to about 310° C., or greater than or equal to about 315°C. and less than or equal to about 390° C., for example, less than orequal to about 380° C., less than or equal to about 370° C., less thanor equal to about 360° C., less than or equal to about 350° C., lessthan or equal to about 340° C., or less than or equal to about 330° C.After or during the heating of the reaction mixture to the secondreaction temperature, a sulfur containing precursor may be injected atleast one time (e.g., at least twice, at least three times).

The reaction time at the second reaction temperature may be controlledappropriately. For example, the reaction time at the second reactiontemperature may be greater than or equal to about 30 minutes, forexample, greater than or equal to about 40 minutes, greater than orequal to about 50 minutes, greater than or equal to about 60 minutes,greater than or equal to about 70 minutes, greater than or equal toabout 80 minutes, greater than or equal to about 90 minutes, and lessthan or equal to about 4 hours, for example, less than or equal to about3 hours, less than or equal to about 2 hours.

In an embodiment, the amount of sulfur with respect to one mole ofindium may be greater than or equal to about 5 moles, greater than orequal to about 6 moles, greater than or equal to about 7 moles, greaterthan or equal to about 8 moles, greater than or equal to about 9 moles,greater than or equal to about 10 moles, greater than or equal to about11 moles, greater than or equal to about 12 moles, greater than or equalto about 13 moles, greater than or equal to about 14 moles, greater thanor equal to about 15 moles, greater than or equal to about 16 moles,greater than or equal to about 17 moles, greater than or equal to about18 moles, greater than or equal to about 19 moles, or greater than orequal to about 20 moles, but is not limited there to. In an embodiment,the amount of sulfur with respect to one mole of indium in a reactionmixture including the particle having the first semiconductornanocrystal shell on the core may be less than or equal to about 45moles, less than or equal to about 40 moles, or less than or equal toabout 35 moles, but is not limited there to.

An amount of the zinc containing precursor with respect to the indiummay be controlled and selected considering the amounts of the seleniumcontaining precursor and the sulfur containing precursor, the propertiesand the structure of the final quantum dot.

When the non-solvent is added into the obtained final reaction solution,the organic ligand-coordinated nanocrystal may be separated (e.g.,precipitated). The non-solvent may be a polar solvent that is misciblewith the solvent used in the reaction and nanocrystals are notdispersible therein. The non-solvent may be selected depending on thesolvent used in the reaction and may be for example, acetone, ethanol,butanol, isopropanol, ethanediol, water, tetrahydrofuran (THF),dimethylsulfoxide (DMSO), diethylether, formaldehyde, acetaldehyde, asolvent having a similar solubility parameter to the foregoing solvents,or a combination thereof. The separation may be performed through acentrifugation, precipitation, chromatography, or distillation. Theseparated nanocrystal may be added to a washing solvent and washed, ifdesired. The washing solvent is not particularly limited and may includea solvent having a similar solubility parameter to that of the ligandand may, for example, include hexane, heptane, octane, chloroform,toluene, benzene, and the like.

The population of the quantum dots may be dispersed in a dispersingsolvent. The population of the quantum dots may form an organic solventdispersion. The organic solvent dispersion may be free of water and/ormay be free of a water miscible organic solvent. The dispersing solventmay be selected appropriately. The dispersing solvent may include (orconsists of) the aforementioned organic solvent. The dispersing solventmay include (or consists of) a substituted or unsubstituted C1 to C40aliphatic hydrocarbon, a substituted or unsubstituted C6 to C40 aromatichydrocarbon, or a combination thereof.

In another embodiment, a quantum dot composition includes: theaforementioned population of the cadmium free quantum dots; apolymerizable (e.g., photopolymerizable) monomer including acarbon-carbon double bond; and optionally a binder polymer; andoptionally an initiator (e.g., a photoinitiator). The composition mayfurther include an organic solvent and/or a liquid vehicle. Thecomposition may be photosensitive.

In the composition, details for the population of the cadmium freequantum dots are the same as set forth above. In the composition, theamount of the quantum dot may be selected appropriately in light of thetypes and amounts of other components in the composition and a final usethereof. In an embodiment, the amount of the quantum dot may be greaterthan or equal to about 1 wt %, for example, greater than or equal toabout 2 wt %, greater than or equal to about 3 wt %, greater than orequal to about 4 wt %, greater than or equal to about 5 wt %, greaterthan or equal to about 6 wt %, greater than or equal to about 7 wt %,greater than or equal to about 8 wt %, greater than or equal to about 9wt %, greater than or equal to about 10 wt %, greater than or equal toabout 15 wt %, greater than or equal to about 20 wt %, greater than orequal to about 25 wt %, greater than or equal to about 30 wt %, greaterthan or equal to about 35 wt %, or greater than or equal to about 40 wt%, based on a total solid content of the composition. The amount of thequantum dot may be less than or equal to about 70 wt %, for example,less than or equal to about 65 wt %, less than or equal to about 60 wt%, less than or equal to about 55 wt %, or less than or equal to about50 wt %, based on a total solid content of the composition.

In the composition of the embodiments, the binder polymer may include acarboxylic acid group (e.g., a carboxylic acid group containingpolymer). In an embodiment, the binder polymer may include:

a copolymer of a monomer combination including a first monomer, a secondmonomer, and optionally a third monomer, the first monomer having acarboxylic acid group and a carbon-carbon double bond, the secondmonomer having a carbon-carbon double bond and a hydrophobic moiety andnot having a carboxylic acid group, and the third monomer having acarbon-carbon double bond and a hydrophilic moiety and not having acarboxylic acid group;

a multi-aromatic ring-containing polymer including a carboxylic acidgroup (—COOH) and having a backbone structure in a main chain (e.g., abackbone structure incorporated in the main chain), wherein the backbonestructure includes a cyclic group including a quaternary carbon atom andtwo aromatic rings bound to the quaternary carbon atom;

or a combination thereof.

Examples of the first monomer may include, but are not limited to,acrylic acid, methacrylic acid, maleic acid, itaconic acid, fumaricacid, 3-butenoic acid, and other carboxylic acid vinyl ester compounds.The first monomer may include one or more compounds.

Examples of the second monomer may include, but are not limited to:

alkenyl aromatic compounds such as styrene, α-methyl styrene, vinyltoluene, or vinyl benzyl methyl ether;

unsaturated carboxylic acid ester compounds such as methyl acrylate,methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate,butyl methacrylate, benzyl acrylate, benzyl methacrylate, cyclohexylacrylate, cyclohexyl methacrylate, phenyl acrylate, or phenylmethacrylate;

unsaturated carboxylic acid amino alkyl ester compounds such as 2-aminoethyl acrylate, 2-amino ethyl methacrylate, 2-dimethyl amino ethylacrylate, or 2-dimethyl amino ethyl methacrylate;

maleimides such as N-phenylmaleimide, N-benzylmaleimide,N-alkylmaleimide;

unsaturated carboxylic acid glycidyl ester compounds such as glycidylacrylate or glycidyl methacrylate;

vinyl cyanide compounds such as acrylonitrile or methacrylonitrile; and

unsaturated amide compounds such as acrylamide or methacrylamide,

but are not limited thereto.

As the second monomer, at least one compound may be used.

If present, examples of the third monomer may include 2-hydroxy ethylacrylate, 2-hydroxy ethyl methacrylate, hydroxy propyl acrylate, hydroxypropyl methacrylate, hydroxy butyl acrylate, and hydroxy butylmethacrylate, but are not limited thereto. The third monomer may includeone or more compounds.

In an embodiment, in the binder polymer, an amount of the firstrepeating unit derived from the first monomer may be greater than orequal to about 5 mole percent (mol %), for example, greater than orequal to about 10 mol %, greater than or equal to about 15 mol %,greater than or equal to about 25 mol %, or greater than or equal toabout 35 mol %. In the binder polymer, an amount of the first repeatingunit may be less than or equal to about 95 mol %, for example, less thanor equal to about 90 mol %, less than or equal to about 89 mol %, lessthan or equal to about 88 mol %, less than or equal to about 87 mol %,less than or equal to about 86 mol %, less than or equal to about 85 mol%, less than or equal to about 80 mol %, less than or equal to about 70mol %, less than or equal to about 60 mol %, less than or equal to about50 mol %, less than or equal to about 40 mol %, less than or equal toabout 35 mol %, or less than or equal to about 25 mol %.

In the binder polymer, an amount of the second repeating unit derivedfrom the second monomer may be greater than or equal to about 5 mol %,for example, greater than or equal to about 10 mol %, greater than orequal to about 15 mol %, greater than or equal to about 25 mol %, orgreater than or equal to about 35 mol %. In the binder polymer, anamount of the second repeating unit may be less than or equal to about95 mol %, for example, less than or equal to about 90 mol %, less thanor equal to about 89 mol %, less than or equal to about 88 mol %, lessthan or equal to about 87 mol %, less than or equal to about 86 mol %,less than or equal to about 85 mol %, less than or equal to about 80 mol%, less than or equal to about 70 mol %, less than or equal to about 60mol %, less than or equal to about 50 mol %, less than or equal to about40 mol %, less than or equal to about 35 mol %, or less than or equal toabout 25 mol %.

In the binder polymer, an amount of the third repeating unit derivedfrom the third monomer, when present, may be greater than or equal toabout 1 mol %, for example, greater than or equal to about 5 mol %,greater than or equal to about 10 mol %, or greater than or equal toabout 15 mol %. In the binder polymer, an amount of the third repeatingunit, when present, may be less than or equal to about 30 mol %, forexample, less than or equal to about 25 mol %, less than or equal toabout 20 mol %, less than or equal to about 18 mol %, less than or equalto about 15 mol %, or less than or equal to about 10 mol %.

In an embodiment, the carboxylic acid group-containing binder mayinclude a copolymer of (meth)acrylic acid and at least one second orthird monomer including an (C6-C9 aryl) or (C1-C10 alkyl)(meth)acrylate,hydroxyl(C1-C10 alkyl) (meth)acrylate, or styrene. For example, thebinder polymer may include a (meth)acrylic acid/methyl (meth)acrylatecopolymer, a (meth)acrylic acid/benzyl (meth)acrylate copolymer, a(meth)acrylic acid/benzyl (meth)acrylate/styrene copolymer, a(meth)acrylic acid/benzyl (meth)acrylate/2-hydroxy ethyl (meth)acrylatecopolymer, a (meth)acrylic acid/benzyl (meth)acrylate/styrene/2-hydroxyethyl (meth)acrylate copolymer, or a combination thereof.

In an embodiment, the carboxylic acid group containing binder mayinclude a multi-aromatic ring-containing polymer. The multi-aromaticring-containing polymer may include a carboxylic acid group (—COOH) anda main chain having a backbone structure incorporated therein, whereinthe backbone structure includes a cyclic group including a quaternarycarbon atom, which is a part of the cyclic group, and two aromatic ringsbound to the quaternary carbon atom. The carboxylic acid group may bebonded to the main chain. The multi-aromatic ring-containing polymer isalso known as a cardo binder, which may be synthesized by a known methodor is commercially available (e.g., from Nippon Steel Chemical Co.,Ltd.).

The carboxylic acid group-containing binder may have an acid value ofgreater than or equal to about 50 mg KOH/g. For example, the carboxylicacid group-containing binder may have an acid value of greater than orequal to about 60 mg KOH/g, greater than or equal to about 70 mg KOH/g,greater than or equal to about 80 mg KOH/g, greater than or equal toabout 90 mg KOH/g, greater than or equal to about 100 mg KOH/g, greaterthan or equal to about 110 mg KOH/g, greater than or equal to about 120mg KOH/g, greater than or equal to about 125 mg KOH/g, or greater thanor equal to about 130 mg KOH/g, but is not limited thereto. Thecarboxylic acid group-containing binder may have an acid value of lessthan or equal to about 250 mg KOH/g, for example, less than or equal toabout 240 mg KOH/g, less than or equal to about 230 mg KOH/g, less thanor equal to about 220 mg KOH/g, less than or equal to about 210 mgKOH/g, less than or equal to about 200 mg KOH/g, less than or equal toabout 190 mg KOH/g, less than or equal to about 180 mg KOH/g, or lessthan or equal to about 160 mg KOH/g, but is not limited thereto.

The binder polymer (e.g., containing the carboxylic acid group, such asthe carboxylic acid group-containing binder) may have a molecular weightof greater than or equal to about 1,000 grams per mole (g/mol), forexample, greater than or equal to about 2,000 g/mol, greater than orequal to about 3,000 g/mol, or greater than or equal to about 5,000g/mol. The binder polymer may have a molecular weight of less than orequal to about 100,000 g/mol, for example, less than or equal to about50,000 g/mol.

In the composition, if present, an amount of the carboxylic acidgroup-containing binder may be greater than or equal to about 0.5 wt %,for example, greater than or equal to about 1 wt %, greater than orequal to about 5 wt %, greater than or equal to about 10 wt %, greaterthan or equal to about 15 wt %, or greater than or equal to about 20 wt%, based on the total weight of the composition. In an embodiment, anamount of the carboxylic acid group-containing binder may less than orequal to about 50 wt %, less than or equal to about 40 wt %, less thanor equal to about 35 wt %, less than or equal to about 33 wt %, or lessthan or equal to about 30 wt %, based on the total weight of thecomposition. The amount of the binder polymer may be greater than orequal to about 0.5 wt % and less than or equal to about 55%, based on atotal solid content of the composition.

In the composition according to an embodiment, the (photo)polymerizablemonomer having at least one (e.g., at least two, at least three, ormore) carbon-carbon double bond may include a (meth)acrylate monomer.Examples of the photopolymerizable monomer may include, but are notlimited to, C1-C10-alkyl (meth)acrylate, ethylene glycoldi(meth)acrylate, triethylene glycol di(meth)acrylate, diethylene glycoldi(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanedioldi(meth)acrylate, neopentyl glycol di(meth)acrylate, pentaerythritoldi(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritoltetra(meth)acrylate, dipentaerythritol di(meth)acrylate,dipentaerythritol tri(meth)acrylate, dipentaerythritolpenta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, bisphenol Aepoxy(meth)acrylate, bisphenol A di(meth)acrylate, trimethylolpropanetri(meth)acrylate, ethylene glycol monomethyl ether (meth)acrylate,novolac epoxy (meth)acrylate, propylene glycol di(meth)acrylate,tris(meth)acryloyloxyethyl phosphate, or a combination thereof.

The amount of the (photo)polymerizable monomer may be greater than orequal to about 0.5 wt %, for example, greater than or equal to about 1wt %, or greater than or equal to about 2 wt % with respect to a totalweight of the composition. The amount of the photopolymerizable monomermay be less than or equal to about 50 wt %, for example, less than orequal to about 40 wt %, less than or equal to about 30 wt %, less thanor equal to about 28 wt %, less than or equal to about 25 wt %, lessthan or equal to about 23 wt %, less than or equal to about 20 wt %,less than or equal to about 18 wt %, less than or equal to about 17 wt%, less than or equal to about 16 wt %, or less than or equal to about15 wt % with respect to a total weight of the composition.

The (photo) initiator included in the composition may be a compound thatcan initiate a radical polymerization of the (photo)polymerizablemonomer and/or a thiol compound (e.g., by light). Types of the initiatorare not particularly limited and may be selected appropriately. Forexample, the initiator may be a photo-initiator and may include atriazine compound, an acetophenone compound, a benzophenone compound, athioxanthone compound, a benzoin compound, an oxime compound, anaminoketone compound, a phosphine or phosphine oxide compound, acarbazole compound, a diketone compound, a sulfonium borate compound, adiazo compound, a diimidazole compound, or a combination thereof, but itis not limited thereto. As an alternative to, or in addition to theforegoing photoinitiators, a carbazole compound, a diketone compound, asulfonium borate compound, an azo compound (e.g., diazo compound), abiimidazole compound, or a combination thereof may be used as aphotoinitiator.

In the composition of the embodiments, an amount of the initiator may beadjusted in light of the types and the amount of the photopolymerizablemonomer as used. In an embodiment, the amount of the initiator may begreater than or equal to about 0.01 wt % or greater than or equal toabout 1 wt % and less than or equal to about 10 wt %, less than or equalto about 9 wt %, less than or equal to about 8 wt %, less than or equalto about 7 wt %, less than or equal to about 6 wt %, or less than orequal to about 5 wt % based on a total weight of the composition, but isnot limited thereto.

The (photosensitive) composition may further include a thiol compoundhaving at least one thiol group (e.g., monothiol or multi-thiolcompound), a metal oxide fine particle, or a combination thereof.

When a plurality of metal oxide fine particles is present in the polymermatrix, the metal oxide fine particles may include TiO₂, SiO₂, BaTiO₃,Ba₂TiO₄, ZnO, or a combination thereof. An amount of the metal oxidefine particle may be less than or equal to about 25 wt %, less than orequal to about 20 wt %, less than or equal to about 15 wt % and greaterthan or equal to about 1 wt %, or greater than or equal to about 5 wt %based on a total solid content of the composition. A particle size ofthe metal oxide fine particles is not particularly limited and may beselected appropriately. The particle size of the metal oxide fineparticles may greater than or equal to about 100 nm, greater than orequal to about 150 nm, or greater than or equal to about 200 nm and lessthan or equal to about 1,000 nm, less than or equal to about 900 nm, orless than or equal to about 800 nm.

The multi-thiol compound may include a dithiol compound, a trithiolcompound, a tetrathiol compound, or a combination thereof. For example,the multi-thiol compound may include glycol di-3-mercaptopropionate(e.g., ethylene glycol di-3-mercaptopropionate), glycoldimercaptoacetate (e.g., ethylene glycol dimercaptoacetate),trimethylolpropane tris(3-mercaptopropionate), pentaerythritoltetrakis(3-mercaptopropionate), pentaerythritoltetrakis(2-mercaptoacetate), 1,6-hexanedithiol, 1,3-propanedithiol,1,2-ethanedithiol, polyethylene glycol dithiol including 1 to 10ethylene glycol repeating units, or a combination thereof.

Based on a total weight of the composition, an amount of the thiolcompound may be less than or equal to about 50 wt %, less than or equalto about 40 wt %, less than or equal to about 30 wt %, less than orequal to about 20 wt %, less than or equal to about 10 wt %, less thanor equal to about 9 wt %, less than or equal to about 8 wt %, less thanor equal to about 7 wt %, less than or equal to about 6 wt %, or lessthan or equal to about 5 wt %. The amount of the thiol compound may begreater than or equal to about 0.1 wt %, for example, greater than orequal to about 0.5 wt %, greater than or equal to about 1 wt %, greaterthan or equal to about 2 wt %, greater than or equal to about 3 wt %,greater than or equal to about 4 wt %, greater than or equal to about 5wt %, greater than or equal to about 6 wt %, greater than or equal toabout 7 wt %, greater than or equal to about 8 wt %, greater than orequal to about 9 wt %, or greater than or equal to about 10 wt %, basedon a total weight of the composition.

The composition may further include an organic solvent and/or a liquidvehicle (hereinafter, simply referred to as “organic solvent”). Types ofthe organic solvent and/or the liquid vehicle are not particularlylimited. Types and amounts of the organic solvent may be appropriatelyselected by considering the aforementioned main components (i.e., thequantum dot, the COOH group-containing binder, the photopolymerizablemonomer, the photoinitiator, and if used, the thiol compound), and typesand amounts of additives which will be described below. The compositionmay include a solvent in a residual amount except for a desired amountof the solid content (non-volatile components). The solvent may beappropriately selected by considering the other components (e.g., abinder, a photopolymerizable monomer, a photoinitiator, and otheradditives) in the composition, affinity for an alkali-developingsolution, a boiling point, and the like. Non-limiting examples of thesolvent and the liquid vehicle may include, but are not limited to:ethyl 3-ethoxy propionate; an ethylene glycol series such as ethyleneglycol, diethylene glycol, or polyethylene glycol; a glycol ether suchas ethylene glycol monomethyl ether, ethylene glycol monoethyl ether,diethylene glycol monomethyl ether, ethylene glycol diethyl ether, anddiethylene glycol dimethyl ether; glycol ether acetates such as ethyleneglycol monomethyl ether acetate, ethylene glycol monoethyl etheracetate, diethylene glycol monoethyl ether acetate, and diethyleneglycol monobutyl ether acetate; a propylene glycol series such aspropylene glycol; a propylene glycol ether such as propylene glycolmonomethyl ether, propylene glycol monoethyl ether, propylene glycolmonopropyl ether, propylene glycol monobutyl ether, propylene glycoldimethyl ether, dipropylene glycol dimethyl ether, propylene glycoldiethyl ether, and dipropylene glycol diethyl ether; a propylene glycolether acetate such as propylene glycol monomethyl ether acetate anddipropylene glycol monoethyl ether acetate; an amide such asN-methylpyrrolidone, dimethyl formamide, and dimethyl acetamide; aketone such as methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK),and cyclohexanone; a petroleum product such as toluene, xylene, andsolvent naphtha; an ester such as ethyl acetate, propyl acetate, butylacetate, cyclohexyl acetate, and ethyl lactate; an ether such as diethylether, dipropyl ether, and dibutyl ether; chloroform, a C1 to C40aliphatic hydrocarbon (e.g., alkane, alkene, or alkyne), a halogen(e.g., chloro) substituted C1 to C40 aliphatic hydrocarbon (e.g.,dichloroethane, trichloromethane, and the like), a C6 to C40 aromatichydrocarbon (e.g., toluene, xylene, and the like), a halogen (e.g.,chloro) substituted C6 to C40 aromatic hydrocarbon, or a combinationthereof.

The composition may further include various additives such as a lightdiffusing agent, a leveling agent, or a coupling agent, in addition tothe aforementioned components. The amount of the additive is notparticularly limited, and may be selected within an appropriate range,wherein the additive does not cause an adverse effect on the preparationof the composition, the preparation of the quantum dot polymercomposite, and optionally, the patterning of the composite. Types andexamples of the aforementioned additives may include any compound havinga desired function and are not particularly limited.

If present, the amount of the additives may be, based on a total weightof the composition (or a solid content of the composition), greater thanor equal to about 0.1 wt %, for example, greater than or equal to about0.5 wt %, greater than or equal to about 1 wt %, greater than or equalto about 2 wt %, or greater than or equal to about 5 wt %, but it is notlimited thereto. If present, the amount of the additives may be lessthan or equal to about 20 wt %, for example, less than or equal to about19 wt %, less than or equal to about 18 wt %, less than or equal toabout 17 wt %, less than or equal to about 16 wt %, or less than orequal to about 15 wt %, but it is not limited thereto.

The composition may be prepared by mixing the aforementioned componentsappropriately. The composition according to the embodiments may providea quantum dot polymer composite or a quantum dot pattern viapolymerization (e.g., photopolymerization).

In an embodiment, a quantum dot polymer composite may include a polymermatrix; and the aforementioned population of cadmium free quantum dotsdispersed in the polymer matrix.

The polymer matrix may include a binder polymer; a polymerizationproduct of a photopolymerizable monomer including at least one (e.g., atleast two, three, four, or five or more) carbon-carbon double bond (s);optionally a polymerization product of the photopolymerizable monomerand a multi-thiol compound having at least two thiol groups at itsterminal ends; or a combination thereof. In an embodiment, the polymermatrix may include a crosslinked polymer and optionally (a carboxylicacid group containing) binder polymer. The crosslinked polymer mayinclude a thiolene polymer, a (meth)acrylate polymer, or a combinationthereof. In an embodiment, the crosslinked polymer may include apolymerization product of the aforementioned photopolymerizable monomerand optionally the multi-thiol compound. Details of the binder polymerare the same as set forth above.

Details of the cadmium free quantum dot, the binder polymer, thephotopolymerizable monomer, the multi-thiol compound are the same as setforth above.

A blue light absorption rate of the quantum dot polymer composite withrespect to light having a wavelength of 450 nm may be greater than orequal to about 82%, for example, greater than or equal to about 83%,greater than or equal to about 84%, greater than or equal to about 85%,greater than or equal to about 86%, greater than or equal to about 87%,greater than or equal to about 88%, or greater than or equal to about89%, for example when an amount of the cadmium free quantum dot is about45% or less based on a total weight of the composite).

The quantum dot polymer composite may be in a form of a film or a sheet.

The film of the quantum dot polymer composite or a pattern thereof mayhave, for example, a thickness of less than or equal to about 30 μm, forexample, less than or equal to about 10 μm, less than or equal to about8 μm, or less than or equal to about 7 μm and greater than about 2 μm,for example, greater than or equal to about 3 μm, greater than or equalto about 3.5 μm, or greater than or equal to about 4 μm.

The sheet may have a thickness of less than or equal to about 1000 μm,for example, less than or equal to about 900 μm, less than or equal toabout 800 μm, less than or equal to about 700 μm, less than or equal toabout 600 μm, less than or equal to about 500 μm, or less than or equalto about 400 μm. The sheet may have a thickness of greater than or equalto about 10 μm, greater than or equal to about 50 μm, or greater than orequal to about 100 μm.

The quantum dot polymer composite may exhibit improved thermalstability. Accordingly, the quantum dot polymer composite may exhibitphoto-conversion efficiency (PCE) of greater than or equal to about 20%,for example, greater than or equal to about 25%, greater than or equalto about 30%, when being heat-treated at about 180° C. for about 30minutes under a nitrogen atmosphere.

In another embodiment, a display device includes a light source and alight emitting element (e.g., a photoluminescent element), and the lightemitting element includes the above quantum dot-polymer composite, andthe light source is configured to provide the light emitting elementwith incident light. The incident light may have a photoluminescencepeak wavelength of greater than or equal to about 440 nm, for example,greater than or equal to about 450 nm and less than or equal to about460 nm.

In an embodiment, the light emitting element may include a sheet of thequantum dot polymer composite. The display device may further include aliquid crystal panel and the sheet of the quantum dot polymer compositemay be disposed between the light source and the liquid crystal panel.FIG. 3 shows an exploded view of a non-limiting display device.Referring to FIG. 3, the display device may have a structure wherein areflector, a light guide panel (LGP) and a blue LED light source(Blue-LED), the quantum dot-polymer composite sheet (QD sheet), forexample, various optical films such as a prism, double brightnessenhance film (DBEF), and the like are stacked and a liquid crystal panelis disposed thereon.

In another embodiment, the display device may include a stackedstructure including a (e.g., transparent) substrate and a light emittinglayer (e.g., a photoluminescent layer) disposed on the substrate as alight emitting element. In the stacked structure, the light emittinglayer includes a pattern of the quantum dot polymer composite, and thepattern may include at least one repeating section configured to emitlight of a predetermined wavelength. The pattern of the quantum dotpolymer composite may include at least one repeating section selectedfrom a first section that may emit a first light and a second sectionthat may emit a second light.

The first light and the second light have a different maximumphotoluminescence peak wavelength in a photoluminescence spectrum. In anembodiment, the first light (R) may be red light present at a maximumphotoluminescence peak wavelength of about 600 nm to about 650 nm (e.g.,about 620 nm to about 650 nm), the second light (G) may be green lightpresent at a maximum photoluminescence peak wavelength of about 500 nmto about 550 nm (e.g., about 510 nm to about 550 nm), or vice versa(i.e., the first light may be a green light and the second light may bea red light).

The substrate may be a substrate including an insulation material. Thesubstrate may include a material such as glass; various polymers such asa polyester (e.g., poly(ethylene terephthalate) (PET), poly(ethylenenaphthalate) (PEN), or the like), polycarbonate, a poly(C1 to C10 alkyl(meth)acrylate), polyimide, polyamide, or a combination thereof (acopolymer or a mixture thereof); polysiloxane (e.g., PDMS); an inorganicmaterial such as Al₂O₃ or ZnO; or a combination thereof, but is notlimited thereto. A thickness of the substrate may be desirably selectedconsidering a substrate material but is not particularly limited. Thesubstrate may have flexibility. The substrate may have a transmittanceof greater than or equal to about 50%, greater than or equal to about60%, greater than or equal to about 70%, greater than or equal to about80%, or greater than or equal to about 90% for light emitted from thequantum dot.

At least a portion of the substrate may be configured to cut (absorb orreflect) blue light. A layer capable of blocking (e.g., absorbing orreflecting) blue light, also referred to herein as a “blue cut layer” or“blue light absorption layer”, may be disposed on at least one surfaceof the substrate. For example, the blue cut layer (blue light absorptionlayer) may include an organic material and a predetermined dye, such as,for example, a yellow dye or a dye capable of absorbing blue light andtransmitting green and/or red light.

In another embodiment, a method of producing the stacked structureincludes

forming a film of the above composition on a substrate;

exposing a selected region of the film to light (e.g., having awavelength of less than or equal to about 400 nm); and

developing the exposed film with an alkali developing solution to obtaina pattern of the quantum dot polymer composite.

The substrate and the composition have the same specification asdescribed above.

A non-limiting method of forming a pattern of the quantum dot polymercomposite is explained with reference to FIG. 4.

The composition is coated to have a predetermined thickness on asubstrate in an appropriate method of spin coating, slit coating, andthe like (S1). If desired, the formed film may be pre-baked (S2).Conditions (such as a temperature, a duration, and an atmosphere) forthe pre-baking may be selected appropriately.

The formed (and optionally, pre-baked) film is exposed to light of apredetermined wavelength (UV light) under a mask having a predeterminedpattern (S3). The wavelength and the intensity of light may be selecteddepending on the types and the amounts of the photoinitiator, the typesand the amounts of quantum dots, or the like.

The film having the exposed selected area is treated (e.g., sprayed orimmersed) with an alkali developing solution (S4), and thereby theunexposed region in the film is dissolved to provide a desired pattern.The obtained pattern may be post-baked (S5), if desired, to improvecrack resistance and solvent resistance of the pattern, for example, ata temperature of about 150° C. to about 230° C. for a predeterminedtime, for example, greater than or equal to about 10 min or greater thanor equal to about 20 min.

When the quantum dot-polymer composite pattern has a plurality ofrepeating sections, a quantum dot-polymer composite having a desiredpattern may be obtained by preparing a plurality of compositionsincluding a quantum dot (e.g., a red light emitting quantum dot, a greenquantum dot, or optionally, a blue quantum dot) having desiredphotoluminescence properties (a photoluminescence peak wavelength andthe like) to form each repeating section and repeating the patternformation process for each of the composition as many times (e.g., twiceor more or three times or more) as required to form a desired pattern ofthe quantum dot polymer composite (S6).

In another embodiment, an ink composition of an embodiment including thepopulation of the cadmium free quantum dots and the liquid vehicle maybe used to form a pattern. For example, a pattern may be formed bydepositing the ink including nanomaterials (e.g., plurality of cadmiumfree quantum dots) and a liquid vehicle and a monomer on a desiredregion of a substrate and optionally removing the liquid vehicle and/orconducting a polymerization.

For example, the quantum dot-polymer composite may be in the form of apattern of at least two different repeating color sections (e.g., RGBsections). Such a quantum dot-polymer composite pattern may be used as aphotoluminescence-type color filter in a display device.

In other embodiments, a display device includes a light source and alight emitting element including a stacked structure.

The light source may be configured to provide incident light to thelight emitting element including the stacked structure. The incidentlight may have a wavelength of about 440 nm to about 480 nm such asabout 440 nm to about 470 nm. The incident light may be the third light.

In a display device including the stacked structure, the light sourcemay include a plurality of light emitting units respectivelycorresponding to the first section and the second section, and the lightemitting units may include a first electrode and a second electrodefacing each other and an electroluminescent layer disposed between thefirst electrode and the second electrode. The electroluminescent layermay include an organic light emitting material.

For example, each light emitting unit of the light source may include anelectroluminescent device (e.g., an organic light emitting diode (OLED))structured to emit light of a predetermined wavelength (e.g., bluelight, green light, or a combination thereof). Structures and materialsof the electroluminescent device and the organic light emitting diode(OLED) are known but not particularly limited.

FIG. 5A and FIG. 5B show a schematic cross-sectional view of a displayof an embodiment of a layered structure. Referring to FIG. 5A and FIG.5B, the light source may include an organic light emitting diode OLED.For example, the OLED may emit blue light or a light having a wavelengthin a region of about 500 nm or less. The organic light emitting diodeOLED may include (at least two) pixel electrodes 90 a, 90 b, 90 c formedon a substrate 100, a pixel defining layer 150 a, 150 b formed betweenthe adjacent pixel electrodes 90 a, 90 b, 90 c, an organic lightemitting layer 140 a, 140 b, 140 c formed on the pixel electrodes 90 a,90 b, 90 c, and a common electrode layer 130 formed on the organic lightemitting layer 140 a, 140 b, 140 c.

A thin film transistor and a substrate may be disposed under the organiclight emitting diode. The pixel areas of the OLED may be disposedcorresponding to the first, second, and third sections that will bedescribed in detail below, respectively.

The stacked structure that includes a quantum dot-polymer compositepattern (e.g., including a first repeating section including green lightemitting quantum dots and/or a second repeating section including redlight emitting quantum dots) and a substrate, or the quantum dot-polymercomposite pattern, may be disposed on or over a light source, forexample, directly on the light source.

The light (e.g., blue light) emitted from the light source may enter thesecond section 21 and the first section 11 of the pattern to emit (e.g.,converted) red light R and green light G, respectively. The blue light Bemitted from the light source passes through or transmits from the thirdsection 31. Over the second section 21 emitting red light and/or thefirst section 11 emitting green light, an optical element 160 may bedisposed. The optical element may be a blue cut layer which cuts (e.g.,reflects or absorbs) blue light and optionally green light, or a firstoptical filter. The blue cut layer 160 may be disposed on the uppersubstrate 240. The blue cut layer 160 may be disposed between the uppersubstrate 240 and the quantum dot-polymer composite pattern and over thefirst section 11 and the second section 21. Details of the blue cutlayer are the same as set forth for the first optical filter 310 below.

The aforementioned device may be fabricated by separately preparing thelayered structure and the OLED (for example, the blue OLED),respectively, and combining them. Alternatively, the device may befabricated by directly forming the pattern of the quantum dot-polymercomposite over the OLED.

In another embodiment, the display device may further include a lowersubstrate 210, an optical element (e.g., polarizer) 300 disposed belowthe lower substrate 210, and a liquid crystal layer 220 interposedbetween the layered structure and the lower substrate 210. The layeredstructure may be disposed in such a manner that a light emitting layer(i.e., the quantum dot-polymer composite pattern) faces the liquidcrystal layer. The display device may further include an optical element(e.g., polarizer) 300 between the liquid crystal layer 220 and the lightemitting layer. The light source may further include an LED andoptionally a light guide panel.

Referring to FIG. 6, in a non-limiting embodiment, the display deviceincludes a liquid crystal panel 200, an optical element 300 (e.g.,polarizer) disposed on and/or under the liquid crystal panel 200, and abacklight unit including a blue light emitting light source 110 under alower optical element 300. The backlight unit may include a light source110 and a light guide 120 (edge type). Alternatively, the backlight unitmay be a direct light source without a light guide panel (not shown).The liquid crystal panel 200 may include a lower substrate 210, an uppersubstrate 240, and a liquid crystal layer 220 between the upper andlower substrates, and a light emitting layer (color filter layer) 230disposed on or under the upper substrate 240. The light emitting layer230 may include the quantum dot-polymer composite (or a patternthereof).

A wire plate 211 is provided on an internal surface, for example, on theupper surface of the lower substrate 210. The wire plate 211 may includea plurality of gate wires (not shown) and data wires (not shown) thatdefine a pixel area, a thin film transistor disposed adjacent to acrossing region of gate wires and data wires, and a pixel electrode foreach pixel area, but is not limited thereto. Details of such a wireplate are known and are not particularly limited.

The liquid crystal layer 220 may be disposed on the wire plate 211. Theliquid crystal layer 220 may include an alignment layer 221 on an uppersurface of the liquid crystal layer 220 and on a lower surface of theliquid crystal layer 220, to initially align the liquid crystal materialincluded therein. Details regarding a liquid crystal material, analignment layer material, a method of forming an alignment layer, amethod of forming a liquid crystal layer, a thickness of liquid crystallayer, or the like are known and are not particularly limited.

In an embodiment, an upper optical element or an upper polarizer 300 maybe provided between the liquid crystal layer 220 and the upper substrate240, but it is not limited thereto. For example, the upper opticalelement or polarizer 300 may be disposed between the liquid crystallayer 220 (or a common electrode 231) and the light emitting layer (orthe quantum dot-polymer composite pattern). A black matrix 241 may beprovided under the upper substrate 240 (e.g., on a lower surfacethereof). Openings within the black matrix 241 are aligned with (orprovided to hide) a gate line, a data line, and a thin film transistorof a wire plate 211 on the lower substrate 210. A second section (R)including a color filter emitting red light, a first section (G)including a color filter emitting green light and/or a third section (B)including a color filter for emitting or transmitting blue light may bedisposed in the openings within the black matrix 241 (BM). For example,the black matrix 241 may have a lattice shape. If desired, the lightemitting layer may further include at least one of a fourth repeatingsection. The fourth section may be configured to emit light having acolor (e.g., cyan, magenta, yellow, or the like) different from thecolors of the light emitted from the first to third sections.

The light emitting layer (color filter layer) 230 may be on atransparent common electrode 231.

If desired, the display device may further include a blue cut filter,hereinafter, also referred to as a first optical filter layer. The firstoptical filter layer 310 may be disposed between upper surfaces of thesecond section (R) and the first section (G) and the lower surface ofthe upper substrate 240, or on an upper surface of the upper substrate(240). The first optical filter layer 310 may include a sheet havingopenings that correspond to the third section (B) (e.g., a pixel areashowing, e.g., emitting, a blue color) and may be formed on portionscorresponding to the first and second sections (G, R). The first opticalfilter layer 310 may be formed as a single body structure over theportions of the light emitting layer 230 corresponding to the first andsecond sections (G, R), and which are other than the portionsoverlapping the third section, but is not limited thereto.Alternatively, at least two first optical filter layers may be spacedapart from each other and may be disposed over each of the portionsoverlapping the first and the second sections, respectively.

For example, the first optical filter layer may block light having apredetermined wavelength range in the visible light range and maytransmit light having another wavelength range. For example, the firstoptical filter layer may block blue light and transmit light other thanblue light. For example, the first optical filter layer may transmitgreen light, red light, or yellow light (e.g., the mixed light of thegreen light and the red light).

The first optical filter layer may include a polymer thin film includinga dye and/or a pigment that absorbs light having a specific wavelength,i.e., the wavelength to be blocked. The first optical filter layer mayblock at least 80%, or at least 90%, even at least 95% of blue lighthaving a wavelength of less than or equal to about 480 nm. With respectto the visible light having other wavelengths, the first optical filterlayer may have a light transmittance of greater than or equal to about70%, for example, greater than or equal to about 80%, greater than orequal to about 90%, or even up to 100%.

The first optical filter layer may absorb and substantially block bluelight having a wavelength of less than or equal to about 500 nm, and forexample, may selectively transmit green light or red light. In thiscase, at least two first optical filter layers may be spaced apart anddisposed on each of the portions overlapping the first and secondsections, respectively. For example, the first optical filter layerselectively transmitting red light may be disposed on the portionoverlapping the section emitting red light and the first optical filterlayer selectively transmitting green light may be disposed on theportion overlapping the section emitting green light.

In an embodiment, the first optical filter layer may include at leastone of a first region and a second region. The first region of the firstoptical filter layer blocks (e.g., absorbs) blue light and red light andtransmits light having a wavelength of a predetermined range, e.g., awavelength greater than or equal to about 500 nm, greater than or equalto about 510 nm, or greater than or equal to about 515 nm, and less thanor equal to about 550 nm, less than or equal to about 540 nm, less thanor equal to about 535 nm, less than or equal to about 530 nm, less thanor equal to about 525 nm, or less than or equal to about 520 nm. Thesecond region of the first optical filter layer blocks (e.g., absorb)blue light and green light and transmits light having a wavelength of apredetermined range, e.g., a wavelength of greater than or equal toabout 600 nm, greater than or equal to about 610 nm, or greater than orequal to about 615 nm and less than or equal to about 650 nm, less thanor equal to about 640 nm, less than or equal to about 635 nm, less thanor equal to about 630 nm, less than or equal to about 625 nm, or lessthan or equal to about 620 nm. The first region of the first opticalfilter layer may be disposed (directly) on or over a locationoverlapping a green light emitting section and the second region of thefirst optical filter layer may be disposed (directly) on or over alocation overlapping a red light emitting section. The first region andthe second region may be optically isolated from one another, forexample, by a black matrix. The first optical filter layer maycontribute to improving the color purity of a display device.

The first optical filter layer may be a reflection type filter includinga plurality of layers (e.g., inorganic material layers) each having adifferent refractive index. For example, in the first optical filterlayer, two layers having different refractive indices may be alternatelystacked on each other. For example, a layer having a high refractiveindex and a layer having a low refractive index may be alternatelylaminated with each other.

The display device may further include a second optical filter layer 311(e.g., red/green light or yellow light recycling layer) that is disposedbetween the light emitting layer 230 and the liquid crystal layer 220,and between the light emitting layer 230—(e.g., the quantum dot polymercomposite layer) and the upper polarizer 300. The second optical filterlayer 311 may transmit at least a portion of a third light, and reflectat least a portion of a first light and/or a second light. The secondoptical filter layer may reflect light having a wavelength of greaterthan 500 nm. The first light may be green (or red) light, the secondlight may be red (or green) light, and the third light may be bluelight.

Another embodiment provides an electronic device including the quantumdot. The device may include a light emitting diode (LED), an organiclight emitting diode (OLED), a sensor, a solar cell, an imaging sensor,or a liquid crystal display (LCD), but is not limited thereto.

Hereinafter, the embodiments are illustrated in more detail withreference to examples. However, the present disclosure is not limitedthereto.

EXAMPLES

Analysis Method

[1] UV-Visible Absorption Analysis

An Agilent Cary5000 spectrometer is used to perform a UV spectroscopyanalysis and UV-Visible absorption spectrum is obtained.

[2] Photoluminescence Analysis

Photoluminescence Analysis is made by using Hitachi F-7000 spectrometerand a photoluminescence spectrum is obtained.

[3] Quantum Yield (QY) of the Quantum Dot

A quantum yield is obtained by dividing the number of the photonsemitted from the sample by the number of the photons absorbed by thesample. It is measured by using QE-2100 (manufactured by Otsukaelectronics Co., Ltd.) with respect to a quantum dot containingdispersion or a quantum dot polymer composite.

[4] Blue Light Absorption Rate and Conversion Efficiency of theComposite

Using an integrating sphere, a light dose of the blue excitation light(B) is measured. Then, a quantum dot polymer composite is placed in theintegrating sphere and is irradiated with the bluet excitation light. Alight dose of green (or red) light emitted from the composite (A) and alight dose of blue light passing through the composite (B′) aremeasured. From the measured values, a blue light absorption rate and thephotoconversion efficiency are calculated by the following equations:Quantum efficiency (QE) of the composite=A/Bblue light absorption rate=(B−B′)/Bphotoconversion efficiency=A/(B−B′)[5] TEM Analysis

A transmission electron microscopic (TEM) analysis is performed usingTitan ChemiSTEM electron microscope.

[6] ICP Analysis

An inductively coupled plasma-atomic emission spectroscopy (ICP-AES)analysis is performed using Shimadzu ICPS-8100.

Reference Example 1

Indium acetate and palmitic acid are dissolved in 1-octadecene in a 200milliliter (mL) reaction flask, subjected to a vacuum state at 120° C.for one hour. A mole ratio of indium to palmitic acid is 1:3. Theatmosphere in the flask is exchanged with N₂. After the reaction flaskis heated to 300° C., a mixed solution of tris(trimethylsilyl)phosphine(TMS₃P) and trioctylphosphine (TOP) is quickly injected, and thereaction proceeds for a predetermined time (e.g., for 20 minutes). Thereaction mixture then is rapidly cooled to room temperature and acetoneis added thereto to produce nanocrystals, which are then separated bycentrifugation and dispersed in toluene to obtain a toluene dispersionof the InP core nanocrystals. The amount of the TMS₃P is about 0.5 molesper one mole of indium. A size of the InP core thus obtained is about2.2 nm.

Example 1

Selenium and sulfur are dispersed in trioctylphosphine (TOP) to obtain aSe/TOP stock solution and a S/TOP stock solution, respectively.

In a 200 mL reaction flask, zinc acetate and oleic acid are dissolved intrioctyl amine and the solution is subjected to vacuum at 120° C. for 10minutes. The atmosphere in the flask is replaced with N₂ while the oleylamine is added thereto. While the resulting solution is heated to about320° C., a toluene dispersion of the InP semiconductor nanocrystal coreare injected thereto and a predetermined amount of Se/TOP stock solutionis injected into the reaction flask over three times. A reaction iscarried out to obtain a reaction solution including a particle having aZnSe shell disposed on the InP core. A total of reaction time is 90minutes.

Then, at the aforementioned reaction temperature, the S/TOP stocksolution and the zinc acetate are injected to the reaction mixture. Areaction is carried out to obtain a resulting solution including aparticle having a ZnS based shell disposed on the ZnSe shell. A total ofreaction time is 70 minutes.

The amounts of Se, S, and Zn used in this example are 16, 12, and 50 per1 mole of Indium, respectively.

An excess amount of ethanol is added to the final reaction mixtureincluding the resulting core/multishell quantum dot, which is thencentrifuged. After centrifugation, the supernatant is discarded, and theprecipitate is dried and dispersed in chloroform to obtain a quantum dotsolution (hereinafter, QD solution).

For the obtained QD solution, a ICP-AES analysis is made, and theresults are shown in Table 1. A photoluminescence spectroscopic analysisand a TEM analysis are made for the QD solution, and the results areshown in Table 2.

A TEM image and a particle size distribution histogram are shown in FIG.7a and FIG. 7B, respectively.

Comparative Example 1

Selenium and sulfur are dispersed in trioctylphosphine (TOP) to obtain aSe/TOP stock solution and a S/TOP stock solution, respectively.

In a 200 mL reaction flask, zinc acetate and oleic acid are dissolved intrioctyl amine and the solution is subjected to vacuum at 120° C. for 10minutes. The atmosphere in the flask is replaced with N₂. While theresulting solution is heated to about 320° C., a toluene dispersion ofthe InP semiconductor nanocrystal core is injected thereto and theSe/TOP stock solution, the S/TOP stock solution, and optionally the zincacetate are injected into the reaction flask over at least three times.A reaction is carried out to obtain a reaction solution including aparticle having a ZnSeS shell disposed on the InP core. A total ofreaction time is 90 minutes.

Then, at the aforementioned reaction temperature, the S/TOP stocksolution and the zinc acetate are injected to the reaction mixture. Areaction is carried out to obtain a resulting solution including aparticle having a ZnS based shell disposed on the ZnSeS shell. A totalof reaction time is 100 minutes.

The amounts of Se, S, and Zn used in this example are 14, 22, and 50 per1 mole of Indium, respectively.

An excess amount of ethanol is added to the final reaction mixtureincluding the resulting core/multishell quantum dot, which is thencentrifuged. After centrifugation, the supernatant is discarded, and theprecipitate is dried and dispersed in chloroform to obtain a quantum dotsolution (hereinafter, QD solution).

For the obtained QD solution, a ICP-AES analysis is made and the resultsare shown in Table 1. A photoluminescence spectroscopic analysis and aTEM analysis are made for the QD solution, and the results are shown inTable 2.

A TEM image and a particle size distribution histogram are shown in FIG.8a and FIG. 8B, respectively.

Comparative Example 2

A population of core-multishell quantum dots is prepared in the samemanner as in Example 1, except that the oleyl amine is not used. A TEManalysis is made for the QD population, and the results are shown inTable 2.

A TEM image and a particle size distribution histogram are shown in FIG.9a and FIG. 9B, respectively.

TABLE 1 Relative mole ratio S + Se/In Zn/In Zn/(Se + S) Comp. Ex 1 26 311.19 Ex 1 22 26 1.18

TABLE 2 Particle size distribution Standard (SD/ FWHM QY averagedeviation solidity Avg. size/) (nm) (%) Size (nm) (SD: nm) Comp. 0.8 42%44 74 6.7 2.8 Ex 1 Ex 1 0.92 15% 36 78 6.0 0.9 Comp. 0.82 over 20% — —6.1 1.6 Ex 2

The results of table 2 confirm that the quantum dots of Example 1 have ahigher value of solidity and a uniform particle size distribution andexhibit a low level of FWHM and enhanced QY.

Experimental Example: Production of a Quantum Dot Polymer Composite anda Pattern Thereof

Each of a chloroform dispersion of the quantum dots of Example 1 and achloroform dispersion of the quantum dots of Comparative Example 1 ismixed with a solution of a binder polymer, which is a four memberedcopolymer of methacrylic acid, benzyl methacrylate, hydroxyethylmethacrylate, and styrene, (acid value: 130 milligrams (mg) per gram ofKOH (mg KOH/g), molecular weight: 8,000 g/mol, acrylic acid:benzylmethacrylate:hydroxyethyl methacrylate:styrene (molarratio)=61.5%:12%:16.3%:10.2%) (solvent: propylene glycol monomethylether acetate, PGMEA, a concentration of 30 percent by weight, wt %) toform a quantum dot-binder dispersion.

To the quantum dot-binder dispersion prepared above, a hexaacrylatehaving the following structure (as a photopolymerizable monomer),ethylene glycol di-3-mercaptopropionate (hereinafter, 2T, as amulti-thiol compound), an oxime ester compound (as an initiator), TiO₂as a metal oxide fine particle, and PGMEA (as a solvent) are added toobtain a composition.

wherein

Based on a total solid content, the prepared composition includes 40 wt% of quantum dots, 12.5 wt % of the binder polymer, 25 wt % of 2T, 12 wt% of the photopolymerizable monomer, 0.5 wt % of the photoinitiator, and10 wt % of the metal oxide fine particle. The total solid content isabout 25%.

The composition obtained above is spin-coated on a glass substrate at150 revolutions per minute (rpm) for 5 seconds (s) to provide a film.The obtained film is pre-baked at 100° C. (PRB). The pre-baked film isexposed to light (wavelength: 365 nanometers (nm), intensity: 100millijoules, mJ) under a mask having a predetermined pattern (e.g., asquare dot or stripe pattern) for 1 s (EXP) and developed with apotassium hydroxide aqueous solution (conc.: 0.043%) for 50 seconds toobtain a pattern of a quantum dot polymer composite (thickness: 6 μm).

The obtained pattern is heat-treated at a temperature of 180° C. for 30minutes under a nitrogen atmosphere. (POB)

For the obtained pattern film, a blue light absorption rate and aquantum efficiency after POB are measured and the results are shown inTable 3.

TABLE 3 Blue light absorption rate (%) QE (%) after POB Comp. Example 192 31 Example 1 84 26

The results of Table 3 confirm that a quantum dot polymer compositepattern including the quantum dots of Example 1 exhibit a higher bluelight absorption rate and a higher quantum efficiency.

The quantum dot polymer composite including the QD of Example 1 mayexhibit a process maintenance ratio of greater than or equal to about95% as determined by a ratio of the Quantum efficiency of the compositeafter POB with respect to QE before POB.

While this disclosure has been described in connection with what ispresently considered to be practical exemplary embodiments, it is to beunderstood that the invention is not limited to the disclosedembodiments, but, on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

What is claimed is:
 1. A quantum dot population comprising a pluralityof cadmium free quantum dots, wherein the plurality of cadmium freequantum dots comprises a semiconductor nanocrystal core comprisingindium (In) and phosphorous (P), a first semiconductor nanocrystal shelldisposed on the semiconductor nanocrystal core and comprising zinc andselenium, and a second semiconductor nanocrystal shell disposed on thefirst semiconductor nanocrystal shell and comprising zinc and sulfur,wherein an average particle size of the plurality of cadmium freequantum dots is greater than or equal to about 5.5 nanometers, astandard deviation of particle sizes of the plurality of cadmium freequantum dots is less than or equal to about 20% of the average particlesize, and an average solidity of the plurality of cadmium free quantumdots is greater than or equal to about 0.85.
 2. The quantum dotpopulation of claim 1, wherein the plurality of cadmium free quantumdots comprises an organic ligand on surfaces thereof, and the organicligand comprises a carboxylic acid compound and a primary aminecompound.
 3. The quantum dot population of claim 2, wherein thecarboxylic acid compound comprises a C5 to C30 aliphatic hydrocarbongroup, and a primary amine group of the primary amine compound comprisesa C5 to C30 aliphatic hydrocarbon group.
 4. The quantum dot populationof claim 3, wherein the primary amine group has a C5 to C30 alkenylgroup.
 5. The quantum dot population of claim 1, wherein the pluralityof cadmium free quantum dots do not comprise boron.
 6. The quantum dotpopulation of claim 1, wherein the first semiconductor nanocrystal shellis disposed directly on the semiconductor nanocrystal core.
 7. Thequantum dot population of claim 1, wherein the first semiconductornanocrystal shell does not comprise sulfur.
 8. The quantum dotpopulation of claim 1, wherein the first semiconductor nanocrystal shellhas a thickness of greater than or equal to about 3 monolayers and lessthan or equal to about 10 monolayers.
 9. The quantum dot population ofclaim 1, wherein the second semiconductor nanocrystal shell is anoutermost layer of the cadmium free quantum dot.
 10. The quantum dotpopulation of claim 1, wherein the second semiconductor nanocrystalshell is disposed directly on the surface of the first semiconductornanocrystal shell.
 11. The quantum dot population of claim 1, whereinthe average particle size of the plurality of the cadmium free quantumdots is greater than or equal to about 5.8 nanometers and the standarddeviation of particle sizes of the plurality of cadmium free quantumdots is less than or equal to about 18% of the average particle size.12. The quantum dot population of claim 1, wherein the average solidityof the plurality of cadmium free quantum dots is greater than or equalto about 0.90.
 13. The quantum dot population of claim 1, wherein amaximum photoluminescent peak of the cadmium free quantum dots has afull width at half maximum of less than or equal to about 40 nanometers.14. The quantum dot population of claim 1, wherein a quantum efficiencyof the plurality of cadmium free quantum dots is greater than or equalto about 70%.
 15. A method of producing the quantum dot population ofclaim 1, which comprises: reacting a zinc containing precursor and aselenium containing precursor in the presence of a semiconductornanocrystal core particle including indium and phosphorous in a heatedorganic solvent and an organic ligand at a first reaction temperature toform a first semiconductor nanocrystal shell on the semiconductornanocrystal core; and reacting a zinc containing precursor and a sulfurcontaining precursor in the presence of a particle having the firstsemiconductor nanocrystal shell formed on the core in the organicsolvent and the organic ligand at a second reaction temperature to forma second semiconductor nanocrystal shell on the first semiconductornanocrystal shell, wherein the organic ligand includes a carboxylic acidcompound and a primary amine compound.
 16. The method of claim 15,wherein the method does not comprise lowering a temperature of areaction mixture including the particle having the first semiconductornanocrystal shell on the core to a temperature below about 100° C.
 17. Aquantum dot-polymer composite comprising: a polymer matrix; and aquantum dot population of claim 1, wherein the plurality of cadmium freequantum dots are dispersed in the polymer matrix.
 18. The quantumdot-polymer composite of claim 17, wherein the polymer matrix comprisesa crosslinked polymer, a binder polymer having a carboxylic acid group,or a combination thereof.
 19. The quantum dot-polymer composite of claim18, wherein the crosslinked polymer comprises a polymerization productof a photopolymerizable monomer including at least carbon-carbon doublebond, a polymerization product of the photopolymerizable monomer and amulti-thiol compound having at least two thiol groups at its terminalend, or a combination thereof.
 20. The quantum dot-polymer composite ofclaim 17, wherein the quantum dot polymer composite comprises aplurality of metal oxide fine particles in the polymer matrix.
 21. Thequantum dot-polymer composite of claim 17, wherein a blue lightabsorption rate of the quantum dot-polymer composite with respect tolight having a wavelength of 450 nanometers is greater than or equal toabout 88% when an amount of the cadmium free quantum dot is about 45%based on a total weight of the composite.
 22. The quantum dot-polymercomposite of claim 17, wherein the quantum dot-polymer composite isconfigured to exhibit a maximum photoluminescent peak with a full widthat half maximum of less than or equal to about 40 nanometers.
 23. Adisplay device, which comprises a light source and a light emittingelement, wherein the light emitting element comprises the quantumdot-polymer composite of claim 17 and the light source is configured toprovide the light emitting element with incident light.
 24. The displaydevice of claim 23, wherein the incident light has a luminescence peakwavelength of about 440 nanometers to about 460 nanometers.
 25. Thedisplay device of claim 23, wherein, the light emitting elementcomprises a sheet comprising the quantum dot polymer composite.
 26. Thedisplay device of claim 23, wherein the light emitting element comprisesa stacked structure including a substrate and a light emitting layerdisposed on the substrate, wherein the light emitting layer includes apattern of the quantum dot polymer composite and the pattern comprisesat least one repeating section configured to emit light at apredetermined wavelength.
 27. The display device of claim 23, whereinthe display device is configured to have a color reproducibility ofgreater than or equal to about 80% measured in accordance with a BT 2020standard.